Question: What is the issue caused that crops up later? When does the game break if this bug does appear?
Answer: I know that there's a high chance you won't be able to enter the prison if you respecced as a demon.
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Question: Is there anything we should look out for that might indicate a corrupted save? Also do you know if it's caused by respeccing to a different mythic path, or is it just respeccing in general?
Answer: If you see mythic quests behaving oddly in later chapters (uninteractable NPCs, non-appearing NPCs, non-opening locations), that is most likely it. It is reported that demon breaks almost 100% if respecced, lich has a relatively high chance, for others chance to get it broken is more or less minor.
Caused by any respec that touches your main character, not just mythic path respec. Companions are not affected.
I've been enjoying WotR very much, it's brilliant despite having some major flaws. This is quite discouraging though.