Orbi RBR750 randomly disconnects/reboots, and loses config settings

My RBR750 randomly reboots 1-2 times per day (that I notice).  This has been happening for around 6 months though seems to have gotten worse in the last 3 months. 

When this happens:

• I leave it for a couple of minutes then the WiFi network reappears. I reconnect to the WiFi, but there is no internet. 
• If I wait another couple of minutes the router will usually reconnect to the internet by itself.  However, sometimes it won't.
• When it doesn't reconnect automatically I connect to the web admin portal for the router and see the setting enabling VLAN/Bridge Settings (required by my ISP) config has gone.  I re-enable it, save settings, and generally within a couple of minutes it will reconnect.  

There is no real pattern to this other than it seems to happen roughly once mid-morning, and once mid/late-afternoon.

My setup:

• RBR750 + 1x RBS750
• Satellite is approx. 10m away from the router.
• House size is 136m2.
• Wireless backhaul.
• Firmware version: V4.6.8.2_2.1.9 (recently upgraded, but didn't fix it)
• Router is running in Router Mode, connected directly to the ISP's ONT via Cat-6 cable.
• ISP is Spark NZ - running 900/500 Mpbs fibre circuit.
• Configured per ISP's recommended settings: How do I set up my NETGEAR router if I have Spark NZ Fibre or UFB? | Answer | NETGEAR Support

Troubleshooting steps taken to date:

• Reboot (obviously)
• Factory reset, re-import previous router config from file.
• Factory reset, manually reconfig router settings.
• Turn off Satellite.
• Turned off any settings I can such as UPnP, private VPN/DNS (go back to ISP DNS), dyn-DNS, etc.
• Changed from 100Mbps to 900Mbps fibre (that has worked a couple of times for me in previous houses with ADSL/VDSL). 

I'm not sure what to do next, but this is really driving me nuts as we often work from home. 

Any help welcome, especially from FURRYe38 

Thanks in advance.