Network consists of Draytek Vigor 2866ax router, Vigor P2100 switch, multiple AP906 WAPs and one AP918R outdoor WAP.
Router and all WAPS have "Home"/"Home51" and "Guest"/"Guest51" SSIDs for 2.4 & 5 GHz with same Home & Guest passwords across all devices
For over 6 months this has been working fine but recently the Guest/Guest51 WiFi  from the AP918R stopped allocating IP to connecting devices, but using Home/Home51 worked fine.
After going to site & noticing a problem with one of the AP906 WAPS, ending up resetting it and reloading the saved config, that WAP is now also failing to allocate IPs to the Guest WiFi.
The WAPs are all connected by ethernet back to the switch (and then to the router) and all are on their latest firmware (which was applied over 6 months ago). I'm the only one with access to change configs, but I've not been onsite since setting them up.
Anyone had similar issues & found a solution?