[2020] MOVED: Safe house lost after trader mission.

No, this is the intended behavior. The point of interest needs to be reset for the quest to work. If it wasn't, you could e.g. demolish a building before triggering the quest, and the courier satchel would be floating in air, or other weird/broken/imbalanced things would happen.

You should take advantage of the bedroll and/or land claim block. These blocks prevent you from starting quests in POIs where you've placed them, among other important benefits.

I'm sorry to read that you lost your stuff.