What is platinum ?

IMHO reasons for such pops and clicks are more to search in other areas
based on my personal experience and based on what I read on RME and other recording forums.

To put some typical examples:

Hardware:
- BIOS settings suboptimal (energy saving, USB settings)
- Mainboard design / chipset
- CPU / GPU design: using Grafic Card inside of the CPU (Intel HD Graphics)
- Not required HW not turned off in the BIOS (i.e. internal sound chip WiFi, Bluetooth)
- How the USB ports are organized internally
- Which USB controller is being used (i.e. USB3, see UFX+ manual)
- Other connected USB devices influencing each other
- On which USB port you plug the device, an USB2 device might run better on a different USB3 port in USB2 compatible mode

Software:
- Immature OS (-> Win10, always changing target my bad uprade policy)
- Internal OS changes after major or even minor release upgrade (Windows and Apple)
- Misbehaving Driver (-> evaluate with LatencyMon)
- Driver killing Harddisk throughput (Intel iaStor driver in my case)
- Drivers allocate CPU resources although they are not required (-> deactivate not required HW in the BIOS)
- impact of certain graphic drivers (eventually a driver update can help=
- Windows settings (energy saving, ..)
- too much load on the system (to many background activities)

Combinations of errors:
- certain combination of HW and Drivers does not perform
- certain combination of connected USB/Fw/ etc external devices does not perform

MMCSS I would regard as "don't care" in this context.
With synchronization this has nothing to do as already made clear by RME support.

See here what i.e. happened to me, not so easy to troubleshoot problem.
Was more or less an occasion / intuition that I found the root cause for my problems:
https://www.forum.rme-audio.de/viewtopic.php?id=20296

I think with your questions in regards to ASIO/MMCSS you are running into a direction
where I never heard that somebody fixed an issue in the area of pops and clicks.

Whats IMHO from you is missing still is an easy to reproduce szenario, when this happens
and a description of surrounding conditions, i.e.:
Does this happen to you only under a real workload?
How does your project look like when you experience this.
How many tracks, VSTs, any virtual instruments in use, which ones ?
Are you working with the DAW or does it simply play back ?

I ask because my problems with the Lenovo Laptop (see link above) also happened,
when the system was under zero load. It was even only a pure playback of a FLAC file
with MusicBee player, using the RME ASIO driver (as MusicBee supports ASIO drivers).

And it happened only when I had in Firefox a webpage loaded and then turned the
scroll wheel on the mouse slightly up and own.
This brought me initially to the idea, that it might have to do with Graphics.
Then I had the idea to use the other GPU in my Laptop, as it had 2, Intel Graphics inside CPU and
a dedicated additional nVidia GPU.
When moving Firefox execution to the nVidia GPU my problems were gone.

So ... this is the reason, why I think its worth that you re-thing and look to
- surrounding conditions
- simplify the error condition to something easily repeatable / reproduceable
which might bring you sometimes to even other ideas and maybe to the root cause of a problem and a solution.

Too sum up.

I would start evaluation completely new.
Start simple.

Do you also have problems with clicks and pops when only playing back a stereo FLAC file with MusicBee
when using RMEs ASIO driver for the Babyface.
Check whether Browsing the Internet brings pops and clocks.
Test whether all possible Buffersizes trigger or mitigate an issue.

If this doesnt bring some reproduceable results, then use your DAW.
Create a simple project.
Playback of a WAV file, nothing else.
Try different ASIO buffersizes.
Add VSTs or other stuff one by the other, in between always experiment with all ASIO buffersizes.
Look where problems do exactly start.

This way you can narrow it down piece by piece I think. Ensure to use latest drivers and Firmware of Babyface.

This approach is based by a strategy to take simply the assumptions

a) with such a small workload nothing bad shall happen no matter which ASIO buffersize you choose
    and it should also be possible to browse the internet and to visit sites with much grafic information
   or many objects on their page. usually I take heise.de for that.

b) if the RME product would be so bad, then the forums (not only RME) would be full of complaints
    and RME wouldnt have the credibility in the market to have the best combination of
    hardware design and high performance / quality drivers. In fact you see only rare complaints
    and its - based on experience - much more likely that the problem is the PC (be it windows or Apple).