Thanks to everyone that helped. It was truly greatly appreciated.

No, can stay that way.

Thank you so much once more.
Mathias, please, would you recommend that I proceed to investigate UFX+ power supply and UFX+ thunderbolt interface now? In terms of the UFX+ power supply, with your help would I be able to look for signs of problems, such as noise, instability, etc. with the oscilloscope I mentioned? I find it interesting that the PS may be under suspicion even if the interface works absolutely fine with USB3. Is TB much more demanding in terms of power?

Should I give up TB and use USB3? What would you do next?

Thanks again.

MC wrote:

See first post. Done already.

Yes, but I tried again with a new set of cable/adapter.

Mathias, I have a question: do I have to restore macOS boot security to use DK TB 1.06 after lowering security level to run KE TB 1.25?

No, can stay that way.

disconnects after around 15 minutes.

Is the unit getting too hot ?
Is one of the adapters getting too hot ?
you have one adapter new and the other is old ? The old one may have issues when getting warm...?

true
then he may wrote by mistake 106 in post 22
or installing all possible drivers all over the place

I tried KE TB 1.25 and DK TB 1.06. But I kept the lowered macOS security level after trying KE TB 1.25 for the first time.

See first post. Done already.

Yes, but I tried again with a new set of cable/adapter.

Mathias, I have a question: do I have to restore macOS boot security to use DK TB 1.06 after lowering security level to run KE TB 1.25?

Intini wrote:

Anything else I should try?

I would test it on a different Mac, just to figure out if it has to do with the Mac (Soft/Hardware) or the UFX+.
Also, I would try different ports on the Mac studio.
Otherwise I would just use it via USB 3 and be happy if everything works that way

That is a great idea, of course. But I don't have another Mac.
Surely, USB3 is my fallback plan. But as I have the UFX+ my biggest motivation to move to a Mac (from PC) was to use TB with the UFX+.  That is why I am spending this time trying to find a solution.

Intini wrote:

I am the OP. I would like to update this thread.
I have been using my UFX+ with USB3 without any problems but decided to nvestigate further the issue with the TB connection.

Following the advice from Mathias to replace all parts in the chain, I found a brand new Apple TB2 to TB3 adapter and a barely used Apple TB 2 cable. I removed all thunderbolt connected devices from the Mac Studio (including SSDs, monitors, etc.), and only left the UFX+ on the thunderbolt ports. I started streaming audio (random YouTube music) and after 16 minutes it disconnected. I used the TB DK driver v1.06 with firmware v112 on the UFX+.

Can I now consider that the problem is with the UFX+, even if USB3 works absolutely fine? Would the power supply affect only the TB? Could it be the TB interface of the UFX+? Anything else I should try?

Why do you use the driver 106 and not the 125 ?

DK125 is for M-Macs, your computer is M4 max Mac

https://rme-audio.de/downloads/driver_tb_mac_125.zip

I just tried again with my recently acquired (used) TB2 cable and the brand new TB2-TB3 adapter with KE driver 1.25. Sadly, it still disconnects after around 15 minutes.

I am the OP. I would like to update this thread.
I have been using my UFX+ with USB3 without any problems but decided to nvestigate further the issue with the TB connection.

Following the advice from Mathias to replace all parts in the chain, I found a brand new Apple TB2 to TB3 adapter and a barely used Apple TB 2 cable. I removed all thunderbolt connected devices from the Mac Studio (including SSDs, monitors, etc.), and only left the UFX+ on the thunderbolt ports. I started streaming audio (random YouTube music) and after 16 minutes it disconnected. I used the TB DK driver v1.06 with firmware v112 on the UFX+.

Can I now consider that the problem is with the UFX+, even if USB3 works absolutely fine? Would the power supply affect only the TB? Could it be the TB interface of the UFX+? Anything else I should try?

Why do you use the driver 106 and not the 125 ?

DK125 is for M-Macs, your computer is M4 max Mac

https://rme-audio.de/downloads/driver_tb_mac_125.zip

Anything else I should try?

I would test it on a different Mac, just to figure out if it has to do with the Mac (Soft/Hardware) or the UFX+.
Also, I would try different ports on the Mac studio.
Otherwise I would just use it via USB 3 and be happy if everything works that way

Following the advice from Mathias to replace all parts in the chain, I found a brand new Apple TB2 to TB3 adapter and a barely used Apple TB 2 cable. I removed all thunderbolt connected devices from the Mac Studio (including SSDs, monitors, etc.), and only left the UFX+ on the thunderbolt ports. I started streaming audio (random YouTube music) and after 16 minutes it disconnected. I used the TB DK driver v1.06 with firmware v112 on the UFX+.

Can I now consider that the problem is with the UFX+, even if USB3 works absolutely fine? Would the power supply affect only the TB? Could it be the TB interface of the UFX+? Anything else I should try?

IMHO there is no other way than to exchange every single part of that chain with another one, one by one, to check if that error goes away. Alternatively if you have access to a different Mac use that one for comparison. Using a multimeter seems pointless, as the breakdown could be caused by a lot of different things, plus is a short-time event that a multimeter most probably will not register.

And one can not exclude the UFX+. Its Thunderbolt port could be defective as well (not that this is a known error, it is not).

Thank you once more.
I mentioned I have an oscilloscope. It is from my home lab: a simple RIGOL DHO924S 4ch 250MHz digital oscilloscope. I don't know if it is fast enough, tough. I mentioned the multimeter because perhaps it could help in checking some fixed voltages from the power supply. I am an electric engineer, if that helps at all. If there is something you believe I could verify, I can try to do it - I can post screen captures from the oscilloscope of some signals if that would help.

If checking the Power Supply and some internal signals is not doable, I would have to buy a TB2 cable and a TB2 to TB3 adapter. But I don't have another Mac to test it. As a side note, I bought the Mac Studio 15 days ago - brand new - but of course there is a possibility that it could be deffective. On the other hand, I tested the TB5 ports on the Mac Studio with an ACASIS TB5 NVMe enclosure with an 8TB SSD and it has been working solidly for many days.

Do you think the first action should be to buy a new cable and adaptor or test some UFX+ signals?

And one can not exclude the UFX+. Its Thunderbolt port could be defective as well (not that this is a known error, it is not).