@NickAG4 

Question, what are those devices?

Ones that have Private Addressing capability?

I see something similar with our Apple devices, iPad, iPhone, and iWatch.

Supposedly, Private Addressing is supposed to use the same MAC address on the same SSID... but sometimes it doesn't seem it does?

I can see connected 'generic' device Icon's with a default name, Tablet, Phone, Watch... and when I dig deeper in the OFF-LINE list I'll find my 'named' device. When I check that device supposedly OFF-LINE, it shows it is ON-Line.

This what seems to work for me:

  @IrvSp Some of them are Apple devices yes, however they all are set to the fixed value already.

I did another network optimization from a different location and the channel was modified and a few other non-apple devices popped in.

  @NickAG4 

Interesting.

Sort of makes me think the could be a Security Issue or connected (or tries to connect) to the 5Ghz SSID which they can't handle?

Also, check the Channel number on both, non-working one could be too high for some devices to 'see'?

When you use the Deco app you can on each known device set the BAND to be used. Also check the Wireless settings to see if the channel setting, should be on AUTO, but you can always move it as the DEFAULT might be on a crowded one?

If using Windows, Acrylic has a FREE LAN Analyzer you can check to see if there is a lot of other devices on it creating some Interference.