There is a mod that is no longer avaliable on the workshop. When you load the world, it will create a file in your saves. Go to your saves folder and look for something along the lines of "[Scenario] Outpost 17 Chapter 0" etc. Select that and click "Edit settings" and view the save's mods. there should be a red number. Select that and remove it from the list. Save the settings and load the world from your saves folder instead of the scenario menu. If this issue occurs on other worlds/scenarios, it should be the same thing.