I've been able to boot into Co-op mode in public matchmaking around maybe a month ago when I got the game, but as of recently it seems like the matchmaking is screwed.
Right now when I try to search for Co-op games it'll show the "Waiting for player to join" gamestate, the BF3 client will start as a background process but it won't actually load into a co-op game regardless of how long I wait in queue. The background client only ever ends up consuming some 43-ish MB of RAM so the game isn't loading anything, CPU usage for BF3 climbs to around 30% after hitting 43 MB RAM usage before dropping down to zero. If I refresh Battlelog, the gamestate disappears but BF3 is still open as a background process. If I wait long enough, I get greeted with "Could not communicate with BF3. Please use the Task Manager to close it down.".
What's up with this? I've used Chrome to boot into matches in the past and its worked fine before, tested to see if disabling Chrome extensions changed anything and it didn't. Wondering if this is an issue with Chrome itself rather than the game.
Edit (Feb 08 2021); It's been a minute. I've tried launching BF3 co-op through Opera GX and it pretty much failed to load into co-op lobbies the exact same way.