Frozen pink picture on external monitor

Hi,

I have a Macbook Pro 2020 (M1) connected to an external monitor via Apple multiport adapter (model #a2119) (hdmi).

It works okay but if I put the Mac to sleep or restart, when it wakes up (sometimes even just when the Mac shuts down), the picture becomes pink and frozen. I can see a cursor and sometimes the top menu, all pink, and can't do anything (waking up the Mac is not possible at this state - it will only wake up when I disconnect the HDMI cable and open the lid on the Mac itself).

The HDMI cable is a high quality one which has never failed me.

Any ideas?

Thank you.