<Solved - (Kind of)> Interface madness... Any wisdom much appreciated

Hello. Here’s a problem that has me properly stumped. Any advice from those more knowledgeable would be very welcome.

The characters: Win 10, Cubase 10.5 Pro, Ableton 10, Studio One 4.0 (basic free version), Fireface UCX interface (connected by USB but never at same time as MR816), Steinberg MR816CSX (connected by firewire but never at same time as Fireface), PC (FX8350 8 core 4.0Ghz, 32Gb RAM, SSDs / Raptors and pretty recent fresh install with everything working nicely. Until…

The issue: I have an old project recorded on an old PC (sadly no longer with us) in Studio One Pro 2.0ish via a Steinberg MR816CSX at 88.2Khz/24bit (Firewire). 85 tracks of audio in total (but only a few playing together at once), no plugins, no processing. All fine and playing nicely at time of recording. I now want to work on it in Cubase 10.5 pro on my new PC running an RME Fireface UCX via USB. I drag and drop all the audio files from Studio one project folder into a brand new Cubase project (before I import, I set the Cubase project settings to 88.2khz / 24bit.) Audio imports into separate tracks no problem and all is sounding fine, with CPU / Disk performance always happily bobbing away well below 10%. After 1-2 mins however, glitches, pops and dropouts arrive and over the course of 5-10 seconds, it sputters out into silence. No performance spike, CPU and disk both quite happy at <10% all the way through this. Software seems to keep playing in the background. If I then reset the Fireface sample buffer to any other value (either higher or lower) it fixes everything and it plays again for a min or two before the exact same thing happens – sputters into silence. This happens at any buffer size (even up to 2048), but the performance meters never go above 10%. Exact same thing happens in Ableton 10 after importing the audio from Studio one into a project there, and also in Studio One when I play the original project. All drivers / Firmware are up to date for everything.

During my trouble shooting efforts so far I have discovered:

  1. If I reconnect and use my old MR816 CSX, there is no issue at all in either Cubase, Studio One or Ableton, even at pretty small buffer sizes (128). This is weird as I would have thought RME FF UCX clocking / drivers would be better than the Steinberg MR816’s
  2. When I open the Cubase media Pool, it says the audio files I have imported are 88.2khz 32 bit floating (not 24bit as per both the original recordings AND the way I specifically set the project up before importing into Cubase project – Cubase seems to have forced them into being 32 bit floating). I have no idea what to make of this – can anyone explain this aspect of bit depth to me?
  3. If I then set the Cubase project to either 32bit floating, or just 32 bit, same problem happens, so doesn’t seem to be the issue.
  4. I’ve tried plugging Fireface into all different USB ports (USB2.0 & USB 3.0) – same issue
  5. If I play any other old project in Cubase (48khz/24bit) – everything is fine, no issues at all.
  6. Have tried disabling all antivirus etc.

I’d be grateful for any wisdom here as my brain is starting to hurt. I can always downsample and work at 48khz but I’m keen to know what the issue is and why a supposedly ‘better’ interface is struggling with this. Anyways, bit of an essay, thanks for taking the time to read and have any suggestions!

Solved - (Kind of)
In case anyone having similar prob, USB seems to be the issue for rme.

When I switch to using the fireface UCX in firewire mode it works fine. Must be some issue with how my PC handles USB lanes. Weird as I did try it in all different USB ports and making sure there was nothing else connected to those ports. Might try getting a dedicated USB PCIE card and see if that avoids the conflict, but for now, its firewire for me…