I currently have a ticket with AppleCare+ about this issue for which I am supposed to receive a call these days. I'll update if there's any valuable output.
But let's face it: As a single consumer it is very difficult to move Apple to do anything. In total, I've spent multiple days debugging, reproducing, and contacting Apple and RME about this issue.
For Apple it took me a lot of frustration, many days, and many tickets to convince them that there is a problem. Finally, one of their employees could match the issue to an internally known one for which there currently is no fix. Now, my support agent is in touch with the engineers working on the issue and is scheduled to provide me with an update during the next days.
From RME's side, the last email that I got, unfortunately, is still in denial even though I pointed them towards the relevant threads in this forum:
RME (on 8 March 2023) wrote:A fundamental problem with the "reliable usability" of the ADI on current or even older Macs can be practically ruled out, nothing of the sort is known or reproducible.
German original:
[E]in grundsätzliches Problem der "verlässlichen Nutzbarkeit" des ADI an aktuellen oder au[c]h älteren Macs lässt sich praktisch ausschließen, es ist nichts dergleichen bekannt oder reproduzierbar.
While I like RME's products a lot and agree with @MC to the extent that I do not suspect a defect/bug on RME's side, I am fed up with the issue being ignored and belittled as a singular issue that one user with some quirky combination of software and hardware has. This is not the case.
To substantiate that: I performed extensive testing, including having my laptop wiped after being checked for any hardware issues by the Apple Store. I was able to reproduce the issue again immediately after the first clean start of the wiped device. Moreover, I can reproduce the issue on my colleague's computer, too.
Just as @kili mentions, using a memory-hungry application is a good way to reproduce the issue. It increases the rate/intensity of the issue, but the issue also is present when memory consumption is low. For instance, I also would observe the issue when I change between two tabs in my browser. Moreover, I noticed that the issue intensifies with higher sample rates (see Audio MIDI Setup app).
RME sells the interface as compatible with macOS. Thus, I expect that I can use my ADI-2 DAC with macOS. RME's responsibility includes the device's compatibility.
At a minimum, I expect RME to:
(1) Help their customers instead of marginalizing and downplaying the issue,
(2) reproduce the issue on their own hardware (get in touch with me if you are not able to),
(3) directly liaise with Apple to pressure them into fixing their issue, and
(4) keep users informed about potential issues and solutions.