A common source for crashes are missing forwarded ports, which result in the game not being able to connect properly. I found that UDP 3659 might be required to play on server (although I’m not sure about that), and some more for hosting Co-Op games.
We tried playing Co-Op in 2023 and after some troubleshooting (for like an hour), we got to the result that we need to forward the following ports: The Source: https://www.tobias-hartmann.net/2011/10/battlefield-3-ports-fur-den-multiplayer-freischalten-portforwarding/
- TCP: 9988, 20000-20100, 22990, 17502, 42127
- UDP: 3659, 14000-14016, 22990-23006, 25200-25300
For the consoles, it seems like you need other ports (listed on the source page).
The ports must of course be opened in the Firewall on your Computer. For us, this didn’t work at first, although we had existing rules for the game. After we deleted the existing rules for Battlefield 3, reopened the game and allowed the firewall to add some rules (the popup that usually comes up when you first open a program), it worked again.
Not sure what was wrong there, but seems like deleting the rules and letting the game re-add them can fix this.