Just wanted to folllow up on this since I figured out over the weekend. I was messing around with Circle on the RBR50 and was having issues with filtering some devices. I assumed it was because the device I was trying to filter wasn't showing as "connected". I upgraded the RBR50 to use NETGEAR Smart Parental Control. This showed me the list of connected devices which was wrong. However the app was now showing me a list of every device ever connected to my network as "Offline Devices" which included devices I was trying to filter. I went ahead and manually deleted all 131 offline devices and then my devices started showing as connected.
I'm guessing devices are getting stuck in offline mode and stop appearing as connected. This is why completely reseting the orbi fixes this issue as it purges this list.
As far as I can tell this list of "offline devices" doesn't appear in the web interfaces but you can get access to this list of devices through the app if you attempt to enable NETGEAR Smart Parental Control. I also saw the list of offline devices in the circle app but there was no way to delete them there.
Hope this helps.