FFA rank not moving?

I’ve played 6 games of ranked ffa since the beginning of op5 (I got master last operation so I was put back to onyx 2) and I’ve won 2 come 2nd twice 3rd once and 5th once and I’ve managed to go down a rank? I went to onyx 1 and then back to onyx 2 I’m sure I should be onyx 3 or diamond 1 actually,I know TC,i know they don’t really care to much but I want to know what’s happening because I should be diamond 1 onyx 3 at leeast