RBR50 WIFI connected no internet and/or WIFI connected, apparently fine, but no internet connection

Hello Community, after almost 4 years of pristine service I am daily encountering the following problem:

1) Wifi connected, no Internet access. Rebooting (turning off Orbi power) all fine for approx 24 hours, then wifi connected but no Internet

2) Happened only once: Wifi connected, Internet access ok (at least no mention of internet access problem) but still no Internet ! Rebooting, all works for a few hours, then back to problem as #1

3) Also devices connected via cable (LAN) do not have Internet access but work fine after rebooting

My system is configured as follows:

Spectrum Modem providing the Internet acces to Orbi RBR50 + 1 Orbi RBS 50 Satellite.

Over 20 devices connected.

Orbis are running with updated firmware V2.7.2.104.

I also did a hard reset on both Orbis (also disconnecting the cables) and a soft rebooting (power off) on the Spectrum Modem.

I read on Internet that router should be changed after 20 000 hours of utilization. Is that the possible cause? Any kind suggestions? Please bear in mind that I am not an IT expert, only very basic know how. Thank you. Federico