The invalid Certificate won't be a cause of your wifi problems.

What Firmware is currently loaded?
What is the Mfr and model# of the ISP modem the NG router is connected too?
Is the Orbi system operating in Router or AP mode?

What is the size of your home? Sq Ft?
What is the distance between the router and satellite(s)? 30 feet is recommended in between them to begin with depending upon building materials when wirelessly connected.

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Try enabling Beamforming and MIMO(MIMO may or maynot be needed) and WMM. Under Advanced Tab/Advanced Settings/Wireless Settings

Try disabling the following and see:
Armor, Circle, Daisy Chain, Fast Roaming, IPv6 and Set 20/40Mhz Coexistence to 40Mhz only. Save settings and reboot the router and satellite(s).

SergeD wrote:
Same issue here...
I reset the orbi rbr50 and satellite to redolve wifi dis connections issue and got an other one with certificate expired
... too much issue in the last months for a 400€ solution....
It has worked fine between sept-dec 2018 but now .... dropping wifi , pages not loading correctly, expired certificate.... if I would know that in advance, i would have choose an other brand, really

Forum Discussion

Netgear Orbi RBK50 - Web certificate expired yesterday (Aug 2, 2019)