Weird issue with new Orbi RBK753, Wi-Fi works fine but loses internet access

I bought a new Orbi RBK753  from Costco on March 30 to replace a dead RBK50.  The RBK753 was working fine until last week.  My configuration:

Orbi is connected to Spectrum Internet (200 mb/s) via an Arris SBS190 cable modem.  The Orbi is configured MAC address security, blocking any devices not on the whitelist from connecting to my Wi-Fi network.  I have a desktop AMD PC connected to one of the LAN ports of the Orbi.  I also have two QNAP NAS servers connected to the other two LAN ports.  I have approximately 30 devices accessing the Orbi Wi-Fi, but only four or five are connected simultaneously.

A couple of weeks ago, my LG Smart TV had a weird error, it said it could connect to the Wi-Fi but it could not access the internet. I reset the TV, reconfigured the Wi-Fi access on the TV and the error persisted.  Finally, I replaced the TV and all was well.  A few days later, a Dell XPS13 laptop encountered the exact same issue, connected via Wi-Fi but no internet access.  Then one of my QNAP NAS servers started having the same issues.

I decided to reboot the cable modem as well as the Orbi router.  The issue persisted. I then shut down the Orbi completely for several minutes and the problem was resolved.  Thinking back, I remembered that my wife's HP Spectre 360 laptop was constantly dropping and reconnecting to the Orbi was well.

I searched online about this issue and see that there are a LOT of owners where the Orbi drops internet but still has Wi-Fi access, but it seems that ALL the devices loses internet access, not just individual devices as in my case.  Router reboots seem to fix their issues.  My question is have any other users encountered the same problems as I have?  If so, how often does this problem occur?

On a side note: I contacted Netgear support to discuss this issue.  Let me be frank, Netgear support was absolutely no help at all. They could not tell me if this is a known issue or if anyone else encountered it.  They said that the system is now working fine and that was it. I know that Netgear only has a 90-day support window so I am worried if this problem pops up again after the 90-day window.  What do owners do when the unit is older than 90 days and the Orbi is still under the one year warranty and cannot get support?

Another question. One user reportedly ended up using the Orbi as an access point, connecting it to another router as a gateway to fix his problem.  If I go that route, can I connected to Orbi using the yellow port to the gateway router as all my other ports are used.