Mac Studio looses Displayconnection after Update from 14.3 to 14.4

My customer is running a MacStudio 23 M2U /128GB about 5m away from the table.

Till yesterday we used a 7,5m HDMI cable to connect a LG Widescreen 34U95.

Sometimes it happened that the display did not show up when powering up the Mac.

But disconnect/connect helped most of the time.

Yesterday I had to erase the Mac (I had migrated from a 2013 machine, looked like I imported something causing hardware freezes) and to reinstall from scratch, using the internal rescue partition.

The system installed OSX new and after that, it was Sonoma 14.4.

The widescreen still worked fine. I further installed Areca Controller (had to reduce security in rescue menu), some editing software like Adobe, BlackMagic Davinci and Avid MediaComposer.

Also some remote software like Teamviewer and Anydesk (I know, but had to).

I kept the machine running over night (as I know Macs are doing strange things overnight, like cleaning up, etc.).

The next morning the display connection was gone. no chance to wake up monitor or mac (the mac basically was up, energy setting was set to always on).

Also replugging the cable did not work.

I connected my Macbook and the Monitor did not show a picture with that 7,5m cable.

I connected a shorter cable, it worked on my book.

I connected a brand new HDMI 2.0 5m cable on the MAc Studio, it did not work.

I connected this cable to the OWC breakout on that Mac Studio, it worked.

I conneted a smaller monitor with the 2.0 5m cable directly to the MAc Studio, it did not show a picture.

Connected the same to the OWC breakout, it works.

So for me it looks like the update from 14.3.x to 14.4. caused an HDMI hardware incompatiblity or a slight reduction in the power-up process of the cable when connected. The display is getting initial information about a newly connected HDMI cable, but after a while it switches off.

So if anybody reading this has a good connection to the developer team, please forward this. regards