You don't have WEP3 enabled in the WiFi security section by any chance? If so switch it off and I think your problem will go away.
I've had problems with my iPhone occasionally asking for a password, and a colleague kept finding his laptop not able to access the internet. Since switching WEP3 off they have all behaved correctly.
I am using AP903's in case it helps in two places, home and work and both places suffered the same issues.

Neil..

My experience with 4 AP903s in a mesh with a 2926ac as the root - serving an iPhone and iPads as well as a number of IOT devices (on a separate VLAN) - with the "WPA2/WPA3" option enabled on the 903s the iPhone (this being the device that moves around more than the others) would fairly frequently pop up the "incorrect password" message. I switched the 903s to WPA2 only and it still does it occasionally, but nowhere near as frequently. Switching wifi off on the phone and back on again resolves the issue. I have no idea why this annoying behaviour occurs.

Interesting and thank you for your response.

I don't have WPA3 enabled on the AP903. Both are set to WPA2.

I've enabled 802.11r over the air and enforced minimum RSSI of -62dBm and that seem to have reduced the number of disconnects and requests for passwords, although we have power outages a few days ago and everything rebooted several times after months of router uptime (the VDSL still disconnects at random early in the morning / late night for no reason)

R