@DeckOh see the solution provided

@Pewill After week and hours of searching, I finally found the solution: switch of the IPv6 functionality in my main router! No errors anymore after this change, stable now for weeks So the...

@David-TP I did not remember the previous version of the firmware, is there a way (log) to find out?

@David-TP Last week I changed the main Deco to an (almost new) other Deco, but the problem remains. I think now that the problem all started with updating the system to the firmware 1.9.1.. Is there...

@David-TP David-TP wrote @Pewill Hi, thank you very much for the feedback. Have you tried to set a different Deco as the main Deco, maybe the "spare, almost-new" Deco M5? How to replace the main Deco...

@David-TP I tested the situation now from saterday up to this day with my new KPN box modem router, but today my wife called me that she had no internet and that the TP-link Deco (the one connected...