Run a speed test to make sure everything is fine in that regard.
You can power cycle your modem, though I doubt the issue is with your equipment.
If the other games are fine, most likely it's either something with the servers or the path your signals are taking to/from the servers. In which case, there's not really anything you can do except wait for it to correct itself (i.e. wait for someone to fix it somewhere along the line of pipes)