Cubase 11 drops an audio interface and connects to another

Hi folks -

I use Cubase on a Mac that also runs Pro Tools. I’d like to use the HDIO on my HDX card as my interface (even though the Avid Coreaudio driver isn’t great) but I keep having an issue where it drops the HDX and then connects to another “interface” I’ve used, namely the headphone out of a Caldigit Thunderbolt breakout box. Anyone else experienced this kind of thing? (before I buy a new Avid cable to test that out.)

2013 Mac Pro, 128 GB RAM, Mojave 10.4.6, Sonnet 3 slot Thunderbolt 2 PCIe chassis, Avid HDX and HDIO, PT2020.11, HD Driver 2020.11, Cubase 11.

In case anyone else is curious:

Replacing the Digilink cable didn’t help. However, cleaning every contact in my Sonnet PCIe chassis and replacing thunderbolt cables with new Apple ones made it disappear almost entirely. This makes me think my issue has mostly to do with Thunderbolt and tiny dropped-data issues . I have a long history of issues with the Thunderbolt situation on my 2013 Mac Pro, and apparently it’s a known issue with these machines. And it appears that the fault-tolerance they have implemented can create other issues with audio chores like maintaining good clocking with interfaces and streaming samples from SSD. When they put out a new one that makes sense to buy (like an Apple Silicon machine with more cores and 256GB RAM) I will maybe go there.