We have 3 AP-900 access points monitored via a Draytek 2860 router. Every so often the AP-900's will drop off the network to varying degrees, sometimes they are still accessible via the admin username and the password I have set and other times they have lost their settings all together.

I have both the 2.4Ghz and 5Ghz WiFi configured. If the units do not loose all their settings, it is normally the 5G network that reverts back to the DrayTek5G default and is disabled.

Really frustrating as I like the kit.

What profiles are you using on the 2860 to manage the APs?
If you are not using the Default then uncheck the auto provision as this will change the settings.
If you are using the Default then I am not sure, are they all on the most recent firmware?

Sorry for the late late reply. I am had Auto provisioning turned on on the AP's but nothing selected in the 2860 AP WLAN PRofiles.

I have not disabled the Auto Provisioning option.

I have each AP setup separately albeit with the same settings apart from the AP Name. The 5G settings got lost again this morning. I can still login using my username and password (Not the default) so it is not a complete reset. but every time there is a problem, the 5G network reverts to the DrayTek5G setting and is disabled. The 2.4Ghz setting remains unchanged, but users do experience connectivity issues, mostly down to not receiving and IP address from the server.