Every time I play, I'll go up a rank, and it'll suddenly disappear. I'll unlock a weapon, and then it will be locked a game or two later. Same with attachments, experience in general, etc.

It's just a mess and I'm getting sick of it.

Glad to see this issue was addressed and others have had the same problem. /sarcasm.

Oh, and whaddya know? I went back on today and I'm rank 19 AGAIN.

I've leveled up to rank 20 three times now.

I can't cross level 9.. When i get level 10 i lose my XP, even if i quit the server and the game say "updating profile", i'm still loosing XP.

it only happens for 2 reasons

1. you were on unranked servers
2. you got disconnected or crashed while playing in ranked servers.