ESP32 not connecting to WiFi Access Point

[TCC-ESP32]

I have a very strange and frustrating problem.
I have four ESP32s and two Access Points on my network.
All the ESP32s are setup the same, exactly the same code, except for server names etc.

So, here's the problem:
I have ESP1, ESP2, ESP3 and ESP4
I have a main router with AP1 and AP2 connected with UTP cable
The network is working fine (as far as I know)
ESP1 is connected to AP1 and working well
ESP2 is connected to AP2 and working well
ESP3 should also connect to AP2 but won't, nor will it connect to AP1. It will connect to the main router.
ESP4 will connect to AP1 and the main router but not to AP2

Now I use the word "connect" loosely because the network says that the ones which won't connect are unreachable, but they show up under the main router's switch settings as being connected to the switch.

If any of this makes sense to someone please let me know because it is driving me crazy.