Steam has apparently changed where Stellaris workshop mods are stored. This is causing a lot of mods not to update properly. Follow these steps to fix the problem:

1. Delete this entire folder from your PC: C:\Users\(Your Name)\Documents\Paradox Interactive\Stellaris\workshop
2. Delete this entire folder from your PC: C:\Program Files (x86)\Steam\SteamApps\workshop\content\281990
3. Unsubscribe from ALL of your Stellaris mods.
4. Resubscribe to all of your Stellaris mods.
5. Open Steam and ensure that it is downloading all of your mods.
6. Run the game after the downloads are complete.

Support for multiplayer related bugs, and mod crashes, will not be given unless you have followed the above instructions first.