I'm using this mat at work along with my Magic Mouse. I've never had an issue with my mouse jumping around or randomly slowing down, but that's exactly what's going on now that I have this mat. Of course I thought it has to be the mouse because that'd make sense, but the mouse works fine if I use it on another surface. The mouse even works fine if I keep it in the center of the desk mat! When the mouse is on the right side of the mat the cursor is jittery, slows down, jumps, everything. I contacted Drop support but they said it's not a defect. I disagree.
The mat feels nice, looks nice, but is causing a super weird issue when the mouse is on the right side.
PS: The mat is basically PR for Varmilo. All the text is talking about them and their switch.
TheOneRawrDid you try rotating the mat around? In my experience Macs are very finicky with BT mice and the symptoms you describe fit perfectly. Rotating the mat around is a simple way to test if the problem is with the right side of the mat.
If it turns out that the problem is indeed with the BT signal, I'd say switch to a Logitech Unifying mouse. The Unifying signal is a lot more reliable.