Educated guess:
You are using a workshop item in an automatch game. Workship items (including skins, faceplates, decals and victory strikes) only work in custom games, this is why it "disappears" when you join a automatch game. The reason it "reappears" after you restart is probably that your load-out is saved.
An alternative would be that you have workshop content disabled in the options.
The all units mod is your friend in this case.
It gives your engineers the ability to built that partisan hut which will allow you built all partisans need for those achievements.