One of The Forgotten quests gives you a "new" hero instead of old injured one. It happens after exploring ruins. On the very same turn this old injured hero got a level up. So I have a message "Hero levelup". I click it AFTER the hero was replaced with new one. I see old skill tree but when I try to see hero statistics or save changes there's an exception. Thankfully the game seems to work ok afterwards.

Would you have an autosave of the game on the turn prior to that quest completion, so we can look at reproducing the issue?