Allright, I went back to an older save, made a few test saves where all units are fortified in different positions, so you only have to press enter to through the turns, and found a save that crashes often. But oddly, it doesn't always crash at the same turn. I started the game and then loaded this save, did this several times, each time just entered through the turns, and it almost always crashes on the second or third turn.
SVN9706 (with /usersettings/customdomadv directory removed, probably not relevant)
I have included the shortdump in the .zip for verification that it has the same crash cause as last time.
No hurry though, I bypassed this crash by regularly saving and loading, and after a while the crash did not happen anymore and I resumed my campaign.