FireFace UCX skipping/stuttering (iMac, latest software and drivers)

[valdikor]

I have an RME FireFace UCX audio interface connected to a 2014 5K Retina iMac with a Fusion Drive and for a few months I have been experiencing very annoying audio skipping/stuttering issue. Here is an example (heard about 4 and 24 seconds in):
https://soundcloud.com/vladobizik/ufx-stuttering/s-spVRa
I doesn’t occur when using the iMac’s internal speakers, it’s isolated to the UCX. I use FireWire (through the Thunderbolt port) for connection but the problem appears also when using USB. It happens at all sample rates, although I think the stuttering is somewhat more pronounced when using higher frequencies.
I tried all the standard troubleshooting measures, e.g. restarting CoreAudio (sudo killall coreaudiod). I have even tried re-installing the system.
I tried connecting my brother’s older FF 400 and it happens with it too. It would seem that the probles is with drivers or the computer, not the specific FireFace device itself. I don’t know where else to look.
It happens with apps playing audio. But it tends to happen more with a pro audio app (e.g. MainStage) open.
I on the latest software, macOS 10.12.5 but it has been occurring since 10.12.3. I am using the latest RME drivers (3.32 in the case of the FW driver).
I have had the interface for years and used it on the same computer for two and a half years and it has only recently started happening.
Is there something I am overlooking, can you help me with the issue?

 

[valdikor]

OK, I seem to have gotten a bit closer to the bottom of this. It does NOT occur on my MacBook Air. However, I installed an older system on an external drive to test with my iMac. I first tried El Capitan 10.11.6 and it worked perfectly. Then I incrementally installed updates. I can confirm it starts occurring with Sierra 10.12.4. It also occurs on the current 10.12.6 beta as well as on the first developer preview of High Sierra. So it seems there is some bug in the system affecting iMacs, maybe related to mechanical drives (the external drive is a spinning one) or Retina Display. Or RME’s drivers need to be updated for recent changes in the OS.

 

[Fishrrman]

RE:
"I first tried El Capitan 10.11.6 and it worked perfectly."

My general rule is:
Go with what works for you.

If you can run 10.11.6, use that -- problems solved.

 

[valdikor]

RE:
"I first tried El Capitan 10.11.6 and it worked perfectly."

My general rule is:
Go with what works for you.

If you can run 10.11.6, use that -- problems solved.

Thanks, that would make sense it the computer was solely a production machine, but it's also my personal machine and I use the Sierra-specific features and I want to continue receiving new features.
I spoke both to Apple and RME support extensively and got nowhere. Seems it’s such a rare problem and I have to hope some future system update fill fix it. In the meantime, it's not that big of a deal, as the I have concluded that the only time it happens noticeably often is when playing audio AND having a DAW open. It doesn't really happen when recording and monitoring or listening to audio when no DAW is open.