CoreELEC 20.1-Nexus Amlogic-ne Discussion

Because I have no current need for DV, I installed CoreELEC20-ne today. First the released 20.1. Because I had problems with wired network I switched to the nightly (CoreELEC-Amlogic-ne.arm-20.1-Nexus_nightly_20230415-Generic.img.gz). Network problems solved.
In the next step I connected with the tvheadend client to the TVHeadend server on my old Wetek Play 2 (running old CoreElec 9.2.8). The public TV channels here in Germany (e.g. ZDF HD) run smoothly, but for some channels I get a strange display, see image. This occurred e.g. for the free private SDTV channels, e.g. SAT-1.
I think I have seen a similar image here on the thread, but could not find it anymore.
Any ideas?