Please try a different USB cable and/or USB-C port. Directly to the Macbook with no hubs.
Also test USB 2.0 mode. See manual and look for "interface mode".

No hubs, directly connected, everything else disconnected. Tried two of the ports, no difference. I am not using USB 2 as I need the Madi channels, that is why I bought the interface in the first place.

I also won't use class compliant mode, as I need TM, which is the other reason why I bought the interface.

Reading for hours through the various posts on this forum I have collected the following info, although nothing is "official"

- M1 USB audio has a problem, Thunderbolt doesn't
- the v3.3 Kernel driver might help, as one can set a higher buffer value, but Apple is discontinuing direct access to the Kernel, which is why RME has driver v4.7
- USB2 has no problems, because less channels mean less data. That is also why other RME interfaces have no problem, like the BabyFace.
- class compliant mode might solve it (not sure why it should, maybe higher buffer settings?) but then TotalMix is not available anymore except through an iPad - more clutter & devices, not less, I don't like it.
- it seems to be an Apple problem that also other interface providers struggle with, but nobody has heard anything from Apple regarding a fix.

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Meanwhile I did a couple more tests. I tried to open a lot of memory-hungry applications and sometimes, audio will stop for several seconds if I do so. ActivityMoniror did not show any memory swapping.

Also, when I play audio, sometimes it doesn't simply stop but does have some distortion before it stops. Looking at what happens to the sine wave test signal, it is very well possible that I hear some distortion in an audio signal before it is shut off.

Obviously, RME won't be able to help much or else this wouldn't be an issue anymore.

It seems to me that issue is not solvable from our end at this time. I will consider the UFX+ instead, which has Thunderbolt.

ups… I was too optimistic. Just had a some crackling with no memory pressure whatsoever, and no load on the CPU. I think the choice is clear. Bye bye UFX III - it was nice while it lasted.  Fingers crossed your 8 year older sibling has what it needs.

Works flawlessly here. No dropouts or sth.

Maybe it had to do sth with your MacOS related config?

Tested with:
UFX III (latest Firmware) connected directly via USB3 to:
MacStudio M1 Max
Sequoia 15.1.1
DK v.4.17

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Edit 2024.12.25:

I just deleted the links to pixshare, as they replaced them (after expiration) with big commercial links to their website.
I don't like to be a spreader of such practices...   
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Thanks - anyhow the topic is closed for you, I just would like to reproduce and understand your issue.

Ok, i did a new test today - tried to max out CPU load, RAM and the USB3 throughput. Believe me or not - i had dozens of apps running at the same time....

Let me describe - all things here were running at the same time:
- UFX III was recording via DUREC to a USB Stick
- Ableton was sending a sine Wave at 0dB and recording the AES Playback to the blue track
- Ableton was set to simulate the max cpu load (80%)
- The clip RAM was also set for all Tracks
- browserbench jetstream was also running
- I even started two instances of an app which played some Audio in Xcode (the red marks in screenshot) to add additional load on cpu, RAM, CoreAudio and the USB3 Bus (one instance on simulator, the other directly on my Mac)

Result:
- I cannot hear or see any dropouts.
- Nothing wron in the durec recording or abletons direct record.
- Cannot confirm this at all.

Let me ask 3 Questions:
Did you really record a sine wave for 2 hours, to look if there are dropouts?
How did you do it (as the browserbench thing just rans for 1,2 minutes)?
How much RAM does your M1 MacBook have?

BTW: I also cannot confirm your statement: "USB2 has no problems, because less channels mean less data. That is also why other RME interfaces have no problem, like the BabyFace."
Because you mix USB2 and USB3 in a total different context.
-> USB2 class spec defines 480 MBit/s transfer rate as maximum. Thats enough for less channel units.
-> While USB3 is specified at 5 GBit/s max. Thats enough to transfer all channels the UFX III needs (if properly connected to a USB3 controller on the Mac).

Here my screens:

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See post number 9
The difference i see is Sonoma vs Sequoia.
As your software runs fine on Sonoma it will have no issues on Sequoia (it is in use now for a time)
Let's hope the upgrade will solve the isseue, unfortunately I don't know any other magic trick.

And there is no guarantee for the fix.
You are right, there is a lot of reports about dropouts, but the huge majority who has no issues and therefore do not report anything, this is invisible.

I'm sorry to hear that, A total fresh install is what I also would do, I guess.

Sonoma and Sequoia behave(d) exactly same here. I just always updated with new releases of MacOS, but never reinstalled a whole system (same for Linux and Windows) for more than 10 years or since the (win95 era is past ;-))...

So, I wonder how the rumor still exists today, by hoping a fresh install will fix everything, instead of trying to get the real cause...

To mention (again) I usually do not do single (one-file) recordings of (multiple) tracks for multiple (or 6 and more) hours.
If you do so, hundreds of reasons can cause dropouts...
Without further details, it is always just a guess. Impossible to give a proofed solution.

Anyhow some examples and tipps, you could check:
- Keeping the (general) formula in mind:
    File size (in bytes) = Sample rate × Bit depth × Channels × Duration (in seconds)
    This would be ~8GB for a 6 hour, stereo, 48kHz, 32bit float recording file (!)
- Afaik (not sure), Spotify usually plays its songs at 44.1kHz? Maybe better to switch your unit to this?
- Do you record into RAM or directly to a file?
- If RAM -> its not endless...  after a while, Mac will cache it to disk (see the swap-thing in this thread)
- Any other processes suddenly get active which affect RAM/Disk writes?
- Any other processes suddenly make use of the same USB controller?
- USB Cable physically 100% OK?
- Tried to raise the buffersize in Pro Tools?
- No other devices or sw that could interfere?
- Checked the RME Settings App for CRC errors?
- Used the Activity Monitor App for an spikes?
- Had a look in the Console App if there are some relevant logs during dropouts?
- etc... etc...

Edit: I addressed this to Tinball.

@fables, yes - i wanted to show that i was not possible to max out my RAM with "usual" apps.

But i am on 64GB RAM here...
Ok - so i just wrote a little bash script, which constantly pumps some data into RAM:

#!/bin/bash

# This script stresses the RAM by allocating memory in blocks of a specified size.

# Function to stress the RAM
stress_ram() {
    local data=()  # Array to hold the data in memory
    local block_size=$1  # Block size in MB passed as an argument
    local block_size_bytes=$((block_size * 1024 * 1024))  # Convert MB to bytes
    local counter=0  # Counter to track the total allocated memory

    echo "Starting RAM stress test with ${block_size} MB per block. Press Ctrl+C to stop."

    # Infinite loop to allocate memory
    while true; do
        # Generate a block of data and store it in the array
        data+=($(head -c "$block_size_bytes" </dev/zero | base64))
        counter=$((counter + block_size))  # Increment the total allocated memory
        echo "RAM usage: ${counter} MB"
        sleep 0.1  # Short pause to make the process observable
    done
}

# Check if block size argument is provided
if [[ $# -eq 0 ]]; then
    echo "Usage: $0 <block_size_in_MB>"
    exit 1
fi

# Call the stress function with the specified block size
stress_ram "$1"

Running the test again (for about 40 Minutes now)...
Till now: No dropouts...
Will post the results when the 64GB are reached.

Edit: Here my result:

It seems that Apple does som kind of magic?
After the RAM was nearly 64 GB, the Mac swaps it to disk. I noticed  it by constantly lowering my free disk space.
Although, the RAM pressure is and was always green. And although my script was constantly pumping data into RAM.

Believe me or not, but i could not find even one dropout in the recorded sine file in ableton.
UFX III was connected via USB3 during this.

fables, (for me) your descriptions are not clear enough to be able to reproduce your issue.
Anyhow, I tried my best, to reproduce your issue while showing what i did as transparent as possible.
But without concrete facts and ability to reproduce what you did... I cannot confirm this at all.

Thanks for sharing