Thanks for replying.
It has been working fine on my Windows 11 Workstation - rock solidly. All I did was disconnect from my Windows 11 Workstation and connect to the Mac Studio. My unit wasn't used that much at all over the short years since I bought it. Very light home studio use. I don't think the issue is after warming up. It disconnects at approximately regular intervals (3-10 minutes) irrespective of the time it has been powered on.
Based on what I read, it is related to macOS Tahoe, the new driver kernel mode security restrictions and changes in the way macOS handles Thunderbolt 2/3 devices.

Thanks for replying.
I am using the kernel extension driver. But I followed all instructions carefully. Maybe it doesn't work in Tahoe? I would prefer the lowest latency for vocal recording - that is why Iwent with the kernel driver. But if this is a known issue with no way to fix it, then I have no choice but to try the driver kit version.
Do you have a similar setup? Is it working for you with the driver kit version of the driver?
Should I abandon the thunderbolt and use only the usb 3 of my ufx+ ?

You are absolutely right. On my Windows 11 workstation I used Totalmix for direct monitoring with some built-in compression, EQ and confort reverb. But I was also able to monitor with relatively low latency (128 samples) through plugins using UAD Luna on Windows 11. But my main motivation to get the M4 Max was to use monitoring through the DAW using UADx plugins. I thought about getting an Apollo for the PC Workstation but decided to get a M4 Max instead for both upgrade the computer and give me near realtime effects for vocal recordings - and keep my beloved RME UFX+. To be fair, on the Mac Studio M4 Max with the RME UFX+ I am being able to record at 32 samples in Cubase if I carefully plan my session - with only low latency plugins in the vocal path all the way through the stereo output. But it is unusable due to the instability. I just need to solve that. I am hoping to be able to keep using the thunderbolt driver in kernel mode if at all possible - or driverkit if not. I can fall back to USB3 - with kernel drivers or with driverkit drivers, if needed.

EDIT: Based on my latest findings, thunderbolt driver only works in kernel mode and USB3 driver only works in driverkit mode.
EDIT 2: I was wrong!!! There are TB and USB drivers for both driverkit and kernel extension.

Thank you, waedi.

I tested the USB3 driver kit option. It works perfectly! I made a test session in Cubase Pro 15, running with 32 samples of buffer, with 5 virtual instruments playing and recording plus the vocal recording with UADx effects, and run it for more than 30 minutes, and didn't get any error or disconnection. Problem solved! It works in USB3!

Having said that, I would appreciate it if someone from RME could let me (us?) know if at some point the thunderbolt connection will work again or if I should just forget it and use only the USB3 instead. I ask this because I understood that with thunderbolt the latency is slightly better - not game changing better, but better nevertheless - and if possible, I would prefer to use it.

Thank you so much. I will try the Driver Kit TB. I revised my previous post.
Do you know if more people had problems with the KE TB driver?

Hi Kubrak,
Thanks for replying.
I did that and it is great. I also use my Focusrite ISA 430MKII as a preamp, EQ, Compressor, etc. It is a very good tool.

But I would like to also be able to use UADx plugins for monitoring. I found that a DAW buffer of 32 samples results in a low enough latency for singing. I was considering an Apollo only for recording vocals but decide to get the fastest computer available and keep using just my RME UFX+ instead. It is actually working fine now. I will try all 4 drivers. Up to now, I tested two drivers: i) TB KE - kept disconnecting; 2) USB3 Driver Kit (works perfectly).

Hi, hselters.
Thanks for replying. I hope to test the TB DK version this weekend. I will post here the outcome.

Hi, Mathias.
Thanks for the reply and the correction. Of course you are right: it was an Apple TB2 cable from UFX+ to the Apple TB2 to TB3 adapter. I have since corrected my post to avoid confusion. I don't have another TB2 cable and TB2 to TB3 adapter to test, unfortunatelly. I know it doesn't mean much but these were almost never used. On Windows 11 I used USB3 - not thunderbolt. The UFX+ worked perfectly on Windows 11 with USB3. I am moving my music workstation from Windows 11 to macOS Tahoe and would like to use thunderbolt, if possible.

I just tried to connect the UFX+ via TB with the DK driver version but unfortunately it still disconnects after some 10 minutes. IF you say it is not the driver, should I buy a new cable to test? Could it be the TB2 to TB3 adapter?

After reading it again, I understand that (every?) one could read it that way. But no. Since my Windows 11 PC had no TB, I used USB3 with it. Please be kind. I am a fan of RME.

Would you please elaborate on how I could check if the problem is with the "extension chassis and its power supply"? If you point me to the instructions on what to look for I could open the unit and check signals with a multimeter and an oscilloscope. Is this a known issue with the UFX+?