ToME: the Tales of Maj'Eyal

Not sure if it's bug, but I have never experienced this before.

Lvl 26 dwarven demonologist, normal roguelike - NO ADDONS (only official DLC's)

After completing anti-antimagic quest, I have decided to move on "Storming the City" quest. I cleared Derth of elementals as usual and went to Angolwen to find Linaniil.
To my surprise, Angolwen was under fog of war again though I already explored it at the beginning. Also, most of the NPC's are missing, including Linaniil.

I am 100% sure I did not use any spells in Angolwen before or summoned any demon.

Is it possible that completing anti-antimagic quest for grand corruptor somehow interacts with mages in angolwen ? If so, there should be some way to use grand corruptor's help to get to the Tempest Peak.

Strange, I also tried to delete zone file for Angolwen multiple times to reset it but the game somehow always remembers it.

Also, I found out that some of the already explored zones (Trollmire, The Maze,..) have been reset completely. Seems like a bug to me.

a boss can only spawn once. and when so happens game remembers it.
when you re-generate a zone, and it comes to spawning them, game is not allowed to spawn a boss the second time.
that "bug" is already known.

as for what caused the zone to re-generate, that is another mater, but we know it happened since it was fogged and missing bosses.

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something reset ALL the zones?

No all, but some. I think this have something to do with messed cloud/local saves, as I usually play ToME on two computers.