Initial bug report:

In my current save, whenever I try to occupy another civilazations site, the game crashes to Desktop as soon as this happens.
Steps to reproduce:
1. Send a few squads to "Demand surrender and occupy" another site. For example select the first six available squads from the list and send them towards Futureace of the Civilazion "Autonomy of Frost" located in the southwest of the map (screenshot attached).
2. Wait for them to leave the map and reach the site.
3. The game crashes before I see any of my military arriving back from the mission.

DF Version is 50.09.
OS is Windows 10.
Save file and screenshot are attached to this bug report.
My game is using multiple mods, but I am unsure how to find out which ones are used in what version for this save in particular. All of them were downloaded from the Steam workshop. Two mods that are definitely included is the Dwarvemon mod and its PMD extension.