So I bled my XT M785 rear brake and it felt great
However the next morning I tried it out again and it felt terrible! Squeaking A LOT also. I presumed that fluid was leaking on the rotor from the calliper but there was no signs of it and also the fluid level seemed to be unchanged.

Any advice?

Leave the bike upside down for a while and then try squeezing the lever, if it goes back to the bars then you still have air in the system/has come back into the system.

I think the piston seals on the calliper are the main culprit if there is a leak.

Cheers mate I’ll give it ago.
Actually it’s got brand new pistons in as the old one cracked!