RBE 770 satellites disconnect from internet

Hi all, I have two RBE 770 satellites connected via LAN cable to the RBE771 router. While the system was running stable over the last months I am experiencing since last week that there is no internet access possible via the satellites WLAN while it is available via the main router WLAN. The satellites show up as connected in the app and sometimes have internet, but then loose it without any apparent reason. When I reboot the RBe 771, I nhave internet for a bit via satellites WLAN, but it disappears quickly the . When connecting the LAN cable of one of the satellites directly to a computer, the same problem appears: first internet is available and then it disappears while the device shows as connected. This makes me think that the internet connection is ok, the satellites are ok, but that there is some problem in the LAN management? Any help would be appreciated.