I'm a new owner of a UCX II, and so far I am quite pleased with the device and software. However, I think I may have encountered a bug in TotalMix FX when I invert the phase of an input routed to a mono output.

Here are the steps to reproduce:
1. In TotalMix FX, raise the level of a mono input in the mix for a mono output.
2. On the device, navigate to the mix screen for that input and output.
3. The Fader level on the device screen matches TotalMix FX and responds to changes to the level in TotalMix FX, as expected.
4. Toggle the phase button in TotalMix FX for that input.
5. The Fader level on the device now shows -∞. I believe this is just a display bug, since I still hear the input coming through.
6. If I change the level in TotalMix FX, it stays at -∞ on the device.
7. When I unplug the device from the computer, the input no longer comes through the output. My guess is that when the device switches to standalone mode, it applies the -∞ from the mix screen.
8. After disconnecting the device, I can restore the level in standalone mode through the device UI, and hear the input again.

I hope this explanation makes sense.

I'm using TotalMix FX 1.85 on macOS, and my UCX II has firmware v106, driver v3.28 B, and SW version 26.

While I'm here, an unrelated small visual quirk I noticed is that for analog inputs 3/4 (line/inst), when instrument mode is on, the reference level setting in TotalMix FX shows +13 dBu/+19 dBu, while the Instrument 3/4 settings screen on the device shows +7 dBu/+13 dBu. The manual mentions that instrument mode raises the sensitivity by 6 dB, so I think +7/+13 is correct.