The MMU2S idler drum is stiff connected with the motor shaft. Both cannot be connected inline perfectly due to part tolerances and the way they connect. 
This induces a variable internal stress during rotation and makes the homing cycle uncertain.
I make use of the original idler drum and a different idler housing + a new flexible motor mount.

The motor mount provides flexibility in 2 rotation vectors. See .pdf with Youtube link, explanation, and print instruction. You can find my .pdf in: https://github.com/prusa3d/Prusa-Firmware/issues/4285    it will link you also to a YouTube video where you can see it working.

I also included an assembly instruction to make sure it applies to the design goals.

My MMU2S works well together with the new FW. I'm interested in result of others. Comments are welcome!