I was getting the same thing, found out an update to the CBA mod was causing a bunch of internal issues, idk if this will help you but what i had to do was uninstall AND UNSUBSCRIBE!!!! (in steam workshop) from the CBA mod and download a previous version (the one i downloaded was the last known working for me v.3.6.1) : https://github.com/CBATeam/CBA_A3/releases/tag/v3.6.1.180131 <---------- Thats the one I used.
Afterward download, extract the files to wherever you have all of your arma3 mods saved ( OS (C:) > Program files (x86) > Steam > Steamapps > workshop content > 107410 for me).
Then finally launch your arma 3 WITHOUT A3 LAUNCHER in steam, go to mods, add local modd, choose the file you manually added to wherever you keep your arma 3 mods, and make sure you check mark every mod you need for the server you are trying to join (you only have to do it once unless you want to play on a server with different mods) and presto!. Now this was situational and might not fix your problem but after 2 days of struggling I found this to be the only thing that fixed my game. However tedious manually checking and unchecking mods from the launcher list is, at least you will be able to play if this works.
(MAKE SURE TO UNSUBSCRIBE IN YOUR WORKSHOP FROM CBA_A3 https://steamcommunity.com/sharedfiles/filedetails/?id=450814997 OTHERWISE STEAM WILL AUTO REINSTALL IT AND YOU WILL HIT THE SAME ISSUE)