I am having the same problem, after the latest patch update in my coop campaign missions the cutscenes will not stop playing and the UI does not come up so I cant play the game. I tried all the DC ACU settings, default, explode etc - turned off all my mods - nothing seems to work.

I have done more testing and and result is quite strange. I have tested at least 2 mission in each category.

1. Normal missions seems to be working, but as DML pointed out some might only work halfway.
2. FAF faction specific missions, also working but same as above.
3. Coalition missions, not working.
4. Seraphim missions, not working.

I remember some time ago the mission Rebels rest had a smiliar problem, the solution was to go into your documents under FAF maps and remove the .v0001 txt (from faf_coop_operation_rebel's_rest.v0001 -> faf_coop_operation_rebel's_rest), since most of the missions in this folder has some version of .v000X txt I have copied the folder and removed the .v000X txt - but this did not work.

I have no advanced skills in coding or programming, but reading through the latest patch notes I could not find anything specific related to mission only changes. Maybe someone in the community with better skills could have a look?