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?
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.