Sound/video desynchronization in playback

[LST]

Hi,
First of all, excuse my English, I hope I'll be understandable... I have a mixing auditorium with :
- Avid S4
- Avid MTRX in video ref
- Avid NEXIS
- MacPro with macOS Catalina
- Blackmagic Design Decklink Studio 4K
- MUTEC iclock dp (video ref)
- JVC video projector

I explain my problem to you, I work with a sound engineer for film mixing and here is the history of what happened :

First thing a little bit strange...
- Copy of the video on the NEXIS, copy session on intern SSD and opening session : ProTools frozen on opening without error message, nor milling...
- New session, import session data : same
- New session, import session data without video, and import video on NEXIS in a second step : PT OK

Here the big problem... :
Sound/image desynchronization on a continuous reading (8 to 12 de-synchronizations suddenly on a 1h50 reading)

Buffer size: 1024 samples
Delay Compensation : On
I restart iclock + MTRX + Mac : same result.
I uncheck GPU Enable in ProTools preference : same result.
Test with an Apple ProRes 422 video, Apple ProRes proxy, DNxHD video: same result.
I tried to pass the video track from FULL Quality to 10bit quality then to Draft : same result.
I can open the Decklink Video Setup preferences from the video track in ProTools, and the video ref is locked to PAL.
Changing the Decklink Video Setup “default video standard” setting to 1080p50 instead of 1080i50: same result.

I tested with another session, another film: everything works fine
Test in sound editing (mac mini) : work fine, so the codec video is fine.

Another problem maybe related...
Video doesn't start sometimes when starting playback, it remains frozen, it starts on the second playback start.

When the video freezes on the videoprojector, it also freezes in the video window of the PT (cmd+9)

I would like to Update 12.2.2 of the Decklink 4K Studio: would correct a problem preventing the synchro start of playback but not Catalina compatible and therefore protools...

Can iClock be at fault? Settings rather vague on the SD/HD settings... Not a lot of menus... but the settings/connections seem coherent.

Globally, I have big doubts about the Blackmagic video capture card...

Do you have any ideas ?

I remain at your disposal for any further information. Thanks in advance everyone !!!!

LST