Kventin
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It looks very much like a problem with incorrectly detecting the Shift key being held down.
A workaround in the game is to Shift + click on any other hero, or simply open the town screen.
To fix this, we need a sequence of actions; the video only shows the problematic situation itself, but not the actions that led to it.
By the way, the save file loaded without any problems; there are no crashes when passing the turn or viewing the opponent's turn.