Orbi RBR850 AP Mode Cisco Switch Network Loop

[80211g]

I have an Orbi RBR850 that was in AP mode for a very long time and things worked well until a few weeks ago. Nothing on my home network changed but all of a sudden the RBR850 kept dropping wifi every few minutes and continues to do so. I'm using the latest firmware (I'm on 4.6.3.16). 

To simplify things I don't even have a satellte connected - just the main router in AP mode connected to a Cisco 3750 switch (IOS 15.0.(2)SE10.

Internet Modem -> Cisco 3750 -> RBR850 in AP Mode -> (wifi clients)

IGMP is disabled and I have confirmed that in the switch config file:

no ip igmp snooping

Yet I continue to have the problem of wifi clients dropping after a few minutes. When I power cycle, or otherwise unplug the network cable from the RBR850 that's connected to the Cisco switch, after the link negotiates on the switchport connected to the Orbi, ALL the other ports on the Cisco switch drop connectivity for a few moments and then come back up normally. However after that, the Orbi still can only keep wifi clients connected for 1-2 minutes before they drop again.

What else can I test or check here to understand the problem? As I mentioned things were working fine in AP mode and I made no changes to my home network. I suppose the Orbi could have automatically updated its firmware during that time. I can leave the Orbi plugged into the same switch and change it to Router mode and things work fine (although now they are double-NATed which is partly why I'm using AP mode)

@FURRYe38 and others.

Thanks!

[CrimpOn]

Would be useful to know what the Cisco switch is connected to. ("Internet Modem").

Unless I am completely mistaken, the Cisco 3750 is a fantastic (but old) 10/100 switch, with amazing switch features, but is not a router or a DHCP server. What is the router?

[80211g]

The "Internet Modem" is a fiber modem in bridge mode which passes a static IP address from my ISP via L2 to a Linux router I have with two interfaces: one external (connected to L2 modem) and one internal (connected to the 3750 switch).

The Linux router provides DHCP services for the LAN including to the Orbi as a mgmt IP address. All other devices that are not on wifi are working fine (i.e. connected directly to the switch via ethernet)

[CrimpOn]

Apart from "I have no idea what could cause this..."

There have been comments on the forum recently about the latest firmware release for the 850 router.  I do not follow them closely because I have only the original (2016) residential 802.11ac Orbi.

If the Orbi is servicing only WiFi clients, I would be interested to know how the "Double NAT" affects those connections.  WiFi clients are unlikely to be targets of Port Forwarding (from the Linux router). Communication with ethernet connected clients could be facilitated with a static route in the LInux router.

And...... what's the point of using only an Orbi router in access point mode?  Is it a need for 802.11ax?  The whole point of Orbi technology would seem to be the "mesh" capabilities.  Do you have a different WiFi router lying around that could replace the Orbi temporarily?  (I have a whole box full of "stuff", including at least three old WiFi routers).

On that Cisco 3750, the tiny LED's on all the other ports actually turn off when the Orbi boots up?

[FURRYe38]

Netgear has set up a community forum specifically for the Orbi AX (WiFi 6) products. Most of the people who watch that forum are more likely to have experience with Orbi AX and know how to work it better than those of us who follow this "general Orbi" forum. Might be more likely to find someone who has a solution if the question is posted there:
https://community.netgear.com/t5/Orbi-AX/bd-p/en-home-orbi-ax

Please use this link to the main forum product list to review and choose where to make your posts. 
https://community.netgear.com/t5/NETGEAR-Forum/ct-p/en-netgear
Thank you