What exactly is the wireless NIC chipset ? model ?
Does it "see" your SSIDs on other of your APs (if you have other models of AP).
 
Historically I think the only times I have seen clients not being able to "see" a SSID has been if the drivers where old, and they did not support newer technologies like 802.11ac / ax and so on.
 
You can still disable for example .ax in your RF profile, but your MR33 is not a .ax AP, so I dont think that is the issue.
 
I have also seen some clients having issues with hidden SSID (and hidden SSID is "NOT a securityfeature(tm)" ) ... so start sending those beacons containing the name if you have disabled that 🙂 )
 
Also, a little related, the band steering feature can cause problems, basically for the same reason.
 
Just my thoughts.
 
/Thomas