Check for worn pulleys or bearings

I am very new to grinding with a 2x72 grinder and have run into a problem. The issue is that when I use a 60 or 80 grit belt with a thick backing everything is fine. When I move up in grits 220 and above where the backing is thinner I run into issues with the belt slipping.

It seems that it is where the tape is joining the belt.
Is this a common issue with you? Are there any workarounds?

The motor and grinder pulleys need to be perfectly parallel or the belt will track to one side or the other. The belt must be uniform with no stretch or wear points which will cause erratic travel. Hope this helps!