hello,try this solution
If you have still problem ..
Please you follow my steps
1.Go to steam library,right click on ETS 2 ,then click on properties
2. Click the DLC tab and un-check all the DLCs which don't work http://prntscr.com/gkc5m1
3. Wait for them to uninstall then check the boxes again for them to install again.
4. Wait for them to install again.
5. Open ETS2 and check that all DLCs work
When you have still a problem?
So again , you follow my steps
1. Go to steam library,right click properties.
2. Click "Verify file integrity" http://prntscr.com/gkc6jb
3. Wait for steam to verify
4. Open the game and test DLCs.
I hope,that this solved your problem
Also you can try uninstall the launcher and install-ed again
1.Please you go to This Computer folder - Program Files - TruckersMP
2.Please you open folder ,which have a name TruckersMP Launcher
3.Next ,there is uninstall , so you click on it Here is photo : https://imgur.com/a/J3cCiGh
4.If you have it done ,then you can go to Documents-ETS 2 MP and ATS MP folders deleted.
5.You have it ?
6.So you can go to Webside TruckersMP - truckersmp.com
7.As next you can downloaded a multiplayer version again . Link is here : https://truckersmp.com/download
Good Luck !!
Best Regards
Soul Knight