I believe there a bug in miRack regarding Link v2 in AUv3. This problem presents in AUM on my iPad Pro first gen 12.9 but not on my iPad Pro first gen 9.7 nor my iPhone 12 mini. On those devices, the stop/start sync works. On all devices, in standalone miRack, Ableton Link is turned on in the setting as is the start/stop sync. Start/stop sync is turned on in the Link v2 module as well.
I have updated everything including the OS of all devices but the same problem persists.
This is frustrating because the 12.9 iPad Pro is my main go between from AUM and my eurorack system for recording and it is how I keep everything in sync.
I hope this can be resolved, any extra information I will endeavour to provide