If it was a change in broadcasting, the problem should happen in all the image. Or that's not the case
No, every driver is different, what triggers an issue in one is unlikely to trigger the same issue in another.
I am pretty sure that the problem is something related to compatibility between vu+ driver (if it's the only box that have the problem) and something like gstreamer or the way it is played.
That does not mean that something is wrong or bugged in enigma2, but just that something is different or use different part of driver that bring that bug, whereas before it was not using it or not this way.
I thought this was about broadcasts?
gstreamer is only used for playback of external media, not for broadcasts, and not for playback of recordings, those are directly send to the SoC for processing in hardware, through the drivers.
What is most likely is that something is received that triggers some sort of race condition in the drivers (unexpected value, buffer overflow, things like that ) that causes the drivers to break. Something that is in recent broadcasts, and wasn't in broadcasts year(s) ago.
It is pointless comparing an OpenPLi 9 with a current broadcast with how OpenPLi 7 behaved 4 years ago, as there are so many things different that makes a comparison pointless..
If you do want to compare, flash OpenPLi 6 or 7, or an old ATV now, and see if you observe the problem.