Ongoing: devices that do not show as connected to WiFi on RBR850 system

Hello, this has been an ongoing issue from time to time over the last 2 weeks. FURRYe38 has been very helpful so far in helping me try some things. The original problem was my wife's iPhone SE appears to disconnect from the WiFi when sleep/do not disturb (DND) is on.

After some more testing, I have the following status/updates:

1. The problem does not happen every day. Sometimes it goes 2-3 days before it happens. Then, it seems ot happen more frequently.

2. I have the latest firmware, V3.2.16.6_1.4.4

3. I have removed, re-added, and sync'd both satellites. The RBR850 is in the basement, the RBS850's are on the first and second floor.

4. I have narrowed the issue down - it appears to happen now only when the iPhone is on the second floor, at the opposite end of the house from the RBS850 on that floor. That's about 45-50' apart I think. So today, I took my iPad, which has never had an issue, and put it in DND, asleep, and left it in the same place. BOOM! Same problem! So it's not the iPhone SE.

5. I started to think this is just a dead spot. But I quickly wake the iPad, and it appears to be on WiFi from looking at the icons at the top of the creen, which I can see immediately.

6. I ran Airport Utility, to scan and see what networks it can find. It sees my network on channel 11 - the 2.4 network - which makes sense as the 5GHz signal may not be good where this device is tucked away on the opposite side of the house. So it sees a good network why does it appear unconnected in the Orbi app and orbilogin.com? Is there a problem that the RBS will not connect a 5GHz device if 5GHz is not a good signal?

7. Just now, I powered off the RBS850 on the 2nd floor, powered it on - it came up and sync'd fine, blue light. I bet I won't see the problem for a couple of days now, we'll see.

What do you think, any ideas how to troubleshoot this further? I am trying to think of a way I can truly determine if the sleeping device is on WiFi or not. None of the device scanners will do I think, because I have been told by one of the utility authors that they build their list from an ARP command, which means the device WAS online in the last 5-10 minutes or so - it's not really ever a true snapshot of what's online *this instant*. I guess I could turn off cellular and ping the device?

So at this point I don't really know if the device is truly offline from WiFi or not. I suspect it is online, and this is some reporting problem. Any ideas on how to proceed? Thanks!