What you see is the so-called FireWire Display Lag, which PreSonus is working on since more than two years without result. I doubt that Smaart shows everything correctly, because Smaart needs a computer with FireWire and the problem is NOT FireWire itself, but UC Surface. Only Capture and Studio One do not have a problem with the FireWire Diplay Lag.
If your Mac is running on the latest OS version, this might explain the freezing problem, but until now there is no explanation for this phenomenon.
Experienced users do NOT recommend to use the latest firmware version on the RM mixers. Better stay with the previous firmware (v9544) and UC Surface 2.0 or 2.1. It is no problem to use newer iOS versions of UC Surface.
You can find a lot of threads about this subject in the Forums (Live Sound / StudioLive RM Series). See link below.