FIFA 21 players are unhappy with the number of issues they are having. One such issue is a Pro Clubs connection lost error, which prevents players from being matched with other players to participate in online matches.
The bug appeared during the early access period of FIFA 21, and it continued in the full version. Threads have popped up on the game's official forums and Reddit page as players search for an official solution to the problem. So far there are over 100 replies in these threads, and the smaller ones are making the rounds. Some players have figured out, on PlayStation 4 at least, that Nat Type 2 ports seem to be a common issue with this bug, but with no confirmation from EA, that's a guess at this time.
After a week of frustrated players beginning to demand full refunds for not being able to access Pro Clubs mode, EA responded on Twitter on October 9 to confirm they were looking into the issue. They hope to have a solution for this soon.
Meanwhile, EA's various Community Managers have attempted to help some users with temporary fixes for the issue. First, EA_Aljo suggested that users unplug their routers and consoles, restart them, and reload FIFA 21 to see if that fixes things.
If that doesn't work, the next step is to change the IP address of the server your game is connected to. For some reason, UK players are placed on US servers, resulting in high ping times and dropped connections. The FIFA European server IP address is 188.8.131.52. If you are in another country with a similar issue, you will need to contact EA Support and open a support ticket to obtain the server IP address for your region.
Finally, if you're playing on a wired connection, where your router is physically connected to your console, try playing FIFA 21 over a wireless connection. Some users, who are plagued by this problem, play with a wired connection, which can cause the connection to bottleneck and stop suddenly.