How did Daiba know that the party would arrive soon?
Silat cites Daiba, stating that "his fortune-tellings predicted it," before explaining that he knew "a beast in chains" would arrive. Daiba was never shown to possess this kind of foresight. In Berserk, the ability to accurately foresee future events is exceptionally rare and is part of what makes characters like Sonia so unique. The continuation provides no explanation for how Daiba acquired this information, nor does it ever address the matter again. As a result, it comes across as a convenient plot device used solely to justify the party being escorted to the Kushan Empire, but it also leaves a dangerous and misled image of where Daiba's powers lie. But this all raises another question: the Kushan Empire?
It's true that there's nothing indicating Daiba has the ability to see into the future. But I would bet the staff are basing this on a misunderstanding of who gave Ganishka advanced information about the appearance of the Falcon of Light, leading to him invading Midland back in Volume 17. They assumed it was Daiba, but there's no reason to assume that.
Quoting @Aazealh , in Volume 22,
Silat says it was a "(大神官様) which means something like a "hierarch" from a religious order. It's very different both from how Silat refers to Ganishka and from how he refers to Daiba (妖術使い in episode 341), so my guess would be that it's someone else entirely."
Personally, I think that Ganishka could have gotten that information from just about anyone, because it was likely related to the Falcon of Light dream that many people across the world received. I don't think it needed to be someone super special like a medium, or for that matter, Daiba.
How does the Kushan empire still exist?
There are two reasons why this doesn't seem plausible. First, Ganishka would almost certainly have committed all the bulk of his forces to the invasion of Midland. He knew exactly who he was up against and understood the stakes involved. Following his defeat, and given his role as a tyrannical ruler whose authority largely held the empire together, the Kushan state would likely have been thrown into chaos. More importantly, however, Fantasia has already occurred. We are explicitly shown that Falconia is the sole safe haven in this new world, which is, of course, entirely according to Griffith's plan. Under those circumstances, a defeated and fractured Kushan Empire should not be able to continue functioning as a stable political entity, otherwise, what's really Griffith's point? This also comes with a bunch of other problems, like why is Silat now the leader of the said Kushan empire? That's not at all what Miura had described him to be, quiet the opposite really.
I think the Kurultai are supposed to be in charge (not Silat), with fatso as the figurehead of that group. But the whole concept of the Kurultai is already nonsensical. Anyone left behind after Ganishka's invasion force departed couldn't possibly have been of much consequence. He ruled over his kingdom with fear. Anyone he suspected of having the capacity of challenging his rule would have been dealt with already. So you're left with rejects. Awesome.
But then, yeah... Fantasia also exists, so ultimately there's no point debating how the Kushan empire should be governed when it shouldn't even exist to begin with.
But what are Silat, Daiba and Rickert even doing there?
It seems to me that the continuation team may have misunderstood what Miura had established for these characters. After successfully escaping Falconia, Silat tells Rickert in episode 339 that they should return to the Bakiraka's hidden village. This makes perfect sense within the context of the story. If any human settlement could realistically survive in the world of Fantasia, it would be a secluded mountain village hidden from the outside world and defended by elite assassins who have spent their entire lives fighting for survival. Instead, the continuation places these characters in what appears to be a functioning Kushan Empire, a setting that not only contradicts the implications of Fantasia but also ignores the destination Miura had already established for them.
@scaler26 already addressed it, but I'll double down a bit: The bakiraka clan were outcasts. Supporting Ganishka's campaign to seize the Falcon of Light was their last chance to regain their former status in the empire, and they failed. So why would they even have an expectation of calling that capital city their home anymore? They've simply sidestepped everything about the history of the Kushan and Bakiraka to fabricate the current scenario.
Hanarr didn't vanish.
Another major inconsistency, as Hanarr is an elf. Only a few episodes earlier, we were shown that even the merrows - beings with no direct connection to Elfhelm itself- disappeared following the island's destruction. By that logic, Hanarr should have vanished as well. Instead, he remains behind without any explanation. This is consistent with the continuation's broader mishandling of the island's inhabitants, most notably the unexplained non-disappearance of Puck and Ivalera.
Hanarr didn't vanish, even though he was a dwarf, but the Volvaba did, even though she's (presumably) a human
The Great Flatulence of the Ethereal World.
In episode 378, Rakshas summons some kind of shockwave that results in a dark tornado, previously exclusive to the path of dragons created by beherits, as a barrier between the corporeal world and the layer of the Ethereal World where the God Hand reside. After this, "trolls" begin rising from the ground out of a nondescript black liquid. We're told that it's akin to the Qliphoth, as if teasing a Slan appearance that never happens. This is once again ignoring Fantasia as a setting, in which ethereal creatures ought to be showing up and destroying everything in there by default. It’s also the first time we’ve seen an apostle being able to conjure ethereal beasts out of nothing, and even behaving like a beherit in the process.
It did look like a fart from somewhere beneath Rakshas' cloak.
A few things though, just because Slan appeared in the Qliphoth doesn't mean she's associated with that particular strata. SHe appeared there because she knew Guts was there. I've seen a few mistranslations of what she says, but she's not implying that the Qliphoth is
hers, just that she can use it to create more creatures, because she's a member of the God Hand with cool powers.
Also, it seems possible to me that they think Fantasia can exist in pockets, not necessarily the new static state of the world. I don't know how else to explain why after the Rakshas fart, only then would creatures suddenly manifest from the streets, and not before. In any case, it's not explained or addressed beyond Daiba's cryptic line that what's happening is beyond the abilities of an apostle.
How can multiple people make a spell stronger?
To fight against the “trolls”, Farnese performs the formation of the four cardinal kings (while chanting the spell incorrectly and forgetting to set the symbols of the 4 elements); in episode 379, this is shown to encompass the entire Kushan palace. Meanwhile in episode 380 the apprentices from Skellig island are also casting the formation of the four, on top of Farnese's, but this time all together. Not only is it overkill, it's also contradictory to how magic works in Berserk: The formation of the four requires the magic user to personally delve into the Ethereal World with their luminous body and request help from the Four Cardinal Kings. It's an act of communication, having the apprentices chanting together should have no bearing on it and makes no sense. Wait... apprentices?
I don't even think they're casting the formation, I think they're just casting other spells to roast the "trolls." And that would have be fine, except, as you already pointed out:
Why are the novices unaffected by the destruction of the island of Skellig?
Against the established principles of magic in the world of Berserk, it was stated in episodes 373/374 that the magic users from Skellig lost their abilities due to its destruction. However, in episode 380, the apprentices are unaffected by this, being incoherent with what the team had set up just a few releases before. Conveniently, the Great Gurus continue to be out of action, which only reinforces the idea that it was a contrivance to write the Gurus off the story all along.
Aazealh hinted at the nature of this misunderstanding in the 373 thread, and after revisiting it, I agree:
Magic is a skill that one learns, as we saw when Farnese became a magician. It's not something innate you have inside you and that can be taken away. This is a complete misunderstanding of the very nature of magic in the world of Berserk. Now, we do get told in episode 345 that some magicians lived near forests of spiritual trees and did "deep magic research based on their enormous spiritual power", like Flora, but that doesn't mean they're dependent on said power. There is simply no reason for this to happen.
- Silat is treated like Royalty
But the truth is quite the opposite, really, as the Bakiraka were of the lowest social class (caste is probably the right word), similar to slaves. The reason being that they had remained loyal to the former royal family before Ganishka took over. The latter recognized their potential for his war effort, which is why he gave them the task of capturing the Falcon in return for a status they previously did not have.
I could imagine a scenario where the remaining survivors of the Kushan empire have rallied around Silat and the Bakiraka, because they're the only human force capable of surviving in this new world. They may have initially balked at the concept of being led by outcasts, but that can be addressed practically and effectively: It's them or death. Of course, I also don't think the grudges within nation-states would have mattered at all among the humans scurrying from place to place like nomads in Fantasia. But that too isn't addressed.
I wouldn't think too much about the "Shadows Die Twice" shenanigans though. It's just crammed in there as a silly reference by Kurosaki.