DHCP issues only on one SSID and on one AP

APs: Unifi AC Pro. Unifi Switch: US-24 layer 2. Aruba Switch: 2930m layer 3. Unifi controller: VM on Windows server. DHCP server: Windows Server domain controller

Hey. We're experiencing an issue were devices connected to one particular VLAN/ SSID can't get a DHCP IP and instead assign themselves APIPA 169.254 addresses. The strangest thing about this is it's seemingly isolated to only one AP in the business - when the same devices connect to the same SSID/ VLAN on different APs in the building they get an IP via DHCP.

Even more stranger and confussing is that devices can SOMETIMES get an IP via the problem AP whilst connected to the problem VLAN - it's seemingly intermittent. At first I thought maybe the problem VLAN has been incorrectly configured on one of the switches between the AP and the DHCP server but, if this was the case, surely the issue wouldn't be intermittent?

I've checked the DHCP server, which is running on our Windows domain controller, and there aren't any errors so it seems like the DHCP requests travelling via the problem AP whilst connected on the problem VLAN aren't even reaching the DHCP server.

I'm not even sure where to start looking from here as no one in the IT department has been at this company for more than 6 months and VERY little has been documented. It seems like the problem AP is able to handle traffic fine for the other VLANs/SSIDs, so other than it being poorly configured to channel 8 on 2.4Ghz radio, the AP seems ok and the DHCP server seems ok as it's able to dish out IPs error free for every other VLANs and even for the problem VLAN so long as devices aren't connected to the problem AP.

Could it be that somehow the DHCP broadcast isn't being relayed between the VLANs on the switches? But if so why would it be intermittent?

If you need more information then please let me know!! I'm happy to elaborate on anything you need me to.