Reset (important, speaking of SC TV 2.0):
the box will be brought back to factory settings. OS / Updates will be reinstalled.
Since the recordings are in the cloud, you won't loose them
Powerline:
Did you change some plugs, longer cable, "Mehrfachstecker" --> don't know the name, means that you have a long cable and a lot of plugs on them 🙂
If yes: do try powerline with nothing else connected to the plug, no lamps, nothing!
Try Ethernet directly from the router (Internet Box) to the SC TV 2.0 Box
If the problems are solved, you known why 😉
Filter: that has nothing to do with IP or not. I guess you need them. You won't need them if you are on fibre.