Fix UniFi Access Point stuck on white/blue/off LED cycle

The UniFi WiFi access points have an LED indicating their status. One mode for them is white/blue/off, which is described to be the TFTP recovery:

The device is in TFTP mode, which is triggered by holding the reset button before applying power, then continuing to hold reset until this White/Blue/Off/repeat sequence is seen. If this is not intentional, check and see if the reset button is jammed, it should click when pushed.
UniFi - LED Color Patterns for UniFi Devices

The has been discussed on the official Ubiquiti forums: UAP Pro flashing white/blue will not stop, cannot be located, is it dead?

There was a similar issue with the UniFi Mesh PRO Access Point (UAP-AC-M-PRO): The unit would just cycle through white-blue-off led pattern. I tried resetting the unit with TFTP recovery, but it would persistently return to the same state after the reset.

The device is an outdoor model, which had been installed on the roof. And since the TFTP recovery is meant to come on when the reset button is held down, it might be that there is a circuit short or something in the reset button (a pinhole).

Since the device was out of warranty and not functional, it was  teared it up and see if it was moist inside. Opening was fairly simple, I recommend opening from the long sides as the chips were easier to click open. Once opened there was no clear indication of water inside the device.

After drying the access point motherboard for two days, there was no change to the faulty behaviour. As a final resort the main board of the WiFi base station was subject to a "reflowing process". This is commonly done with motherboards and has been known to revive broken electronic devices: How to Reflow a Laptop Motherboard

After baking the circuit board of the UniFi Mesh AP for 5 minutes in 190 degrees celsius and having cooling down the unit functioned normally again. This is not recommended, but for some extreme cases it might be a functional last-resort fix.