Tvheadend

You need to figure out first where the issue appears, SAT-IP server, network or client. Use Wireshark or tcpdump for that.

Thanks for the feedback.
But this level of sophistication is beyond my abilities. Sure I can install those tools but then for what should i look for?
I can allthough exclude the sat-ip Server because in a different setup it is working flawlessly.

You need to look for continuity errors in the stream, in Wireshark you have a RTP analyzer that will do it for you (to make things easy start the capture before starting the stream, then it will properly detect the stream and you don't have to manually find it).

If the 'uncorrected errors' counter in the streaming status tab is being increased, it's mostly UDP/RTP packet loss. You need to tune your linux/windows settings to deliver all UDP packets to the tvheadend.

it seems that the version 4.2.7 is not affected.
Could you please provide instruction to install an old version.

I am experiencing issues both on Armbian and on Windows.
A raspberry 3 and a synology (DS218+) it is working flawlessly using the same tuner and same network.
I have given up on windows (nextpvr is also not working).

Could you provide some help/hints on Linux (Armbian) on "how to tune linux setting to deliver all UDP packets to the tvheadend"

You should first of all make sure if they ever reach the host using Wireshark/tcpdump, then you can check if they are dropped by the OS. If your hardware is never seeing them it's pointless to tune any settings.

Fiddling around with Wireshark/tcpdump is not what I want. Maybe I will time to try this in the distant future when I have nothing better to do.
Meanwhile I unfortunately have to accept the status quo.

Maybe someone in the forum will support me downgrading tvheadend to version 4.2.7 which seems to work even on a much slower machine.