Sound interruptions, connection with Fireface UCX, connection with external sound sources via USB,

I have three problems.
One is that Cubase repeatedly breaks up the sound.
The second is a problem when connected to the Fireface UCX.
The third is the USB connection for external synths.

The first problem is that Cubase breaks off the sound more times than not, how about you guys?

The second problem is related to the Fireface UCX, when watching Youtube, the audio and images start to break up after about 3-5 minutes. At first I thought it was just a problem with the Fireface UCX. But when I start up Cubase (without starting the project…) when the sound is choppy and the images are choppy, for some reason Youtube becomes normal.
When I play the sound on the speakers of the monitor (video) without using the Fireface UCX, there is no problem, so there seems to be no problem with my PC system. Of course I am not using the Yamaha Steinberg USB Driver, and the Fireface UCX driver is the latest one.

The third problem is that when Cubase and YAMAHA S90XS are connected via USB, the VST of YAMAHA S90XS is not connected properly when launching a pre-Cubase 12 project in Cubase However, if I start a new project in Cubase (after restarting Cubase), select “Empty” from “Others” and start the VST of YAMAHAS 90XS, it starts correctly. Also, in that state, a pre-Cubase 12 project can be connected to the YAMAHAS 90XS without any problems.

Can you guys tell me what is the cause of this mystery?

Sounds like the audio buffer serting is too low.

By the audio buffer serting, you mean Buffer Size, right?
If you set the Buffer Size to 1024 Samples, the result is the same.

Might check Real Time Latency conflicts. NVIDIA drivers can cause some RTP glitches.

Does NVIDIA High Definition Audio or NVIDIA Virtual Audio Device (Wave Extensible) (WDM) in Device Manager also cause problems?

I disabled both NVIDIA High Definition Audio and NVIDIA Virtual Audio Device (Wave Extensible) (WDM), but unfortunately there was no improvement.