Following this process Axis belt adjustment tutorial (I had some Z artifacts) I found out that my gantry belt parallelism is off by a lot. I tried adjust it but with little to no change.
So I tried to loosen belt entirely, and even when belt lie loose, belt tensioner with both side screws removed does not move, next I tried to move tensioner a little with finger and that I heard pop sound and saw that mechanism moved backwards
I think that this hole is to tight and lock tensioner in place
I did contact SOVOL via mail regarding parallelism, but I advise you to check if your tensioners even move on AB axis belt.