Hello, it says "This server's player stats are not tracked. To track player stats, please claim this server." on the server but I claimed the server. I have no option to turn on player tracking or anything.

Moved: Not a Gametracker bug.

As you haven't specified, I will presume you are referring to this server: https://www.gametracker.com/server_info/51.38.35.106:28960 ?

If so, you have only just claimed it.
Historical player statistics are not instantaneously recorded.
Additionally a player must have been in the game playing and have a score, and play for long enough that the server has been scanned while they are playing (with a score) before they will be recorded.

It will likely take at least an hour, perhaps longer, before historical statistics are recoded.

I have the same issue as well on one of my recently added server and I've already played a few matches and still nothing.