RBR850 Internet disconections

I also run in AP mode and had the same issue.  Have you watched the WiFi signal to see if it comes up (in my case the main, IOT, and guest all came up even though I didn't use either of those last two), then they would disappear, then about a minute later they'd come up again.  In my case it was because my pfSense box was blocking ICMP replies to the RBR.  If the RBR can't get an echo reply from whatever is upstream of it, it would just reboot over and over thinking the internet was down.  I allowed ICMP echo replies and it worked from that point on.  Odd obscure issue, but it fixed it for me.