Ok
European power levels are 20 dBm (100mW) in 2.4 and 30 dBm (1000 mW).
In open spaces a laptop will connect in 5 GHz to an AP-175 up to 600m away using the 5 dBi omni kit ANT-2x2-5005.
The 607 has a couple dB more gain at its peak and your deployment is directionally oriented.
Your comments indicate that this is a global issue so this is not an issue with a single client device.
These are my assumptions but I will ask to verify
AP-175
No lightning surge protectors
2 x ANT-2x2-D607 on each AP-175 with no other cables. Pigtails only.
The pigtail cables are not stretched in install and not stressed
The cables were not used as handles when the antennas were installed
The antennas are mounted on a wall
The antennas are installed with the cables coming out the bottom
The back plate of the antenna is installed parallel with the wall.
CSD override disabled
Ant gain set to 7 in both bands
Tx power (EIRP) set to 20 dBm in 2.4 and 30 dBm in 5 GHz.
The only mechanism that I am aware of that can create a global failure would be a very high power transmitter operating between 3 and 4 GHz or individual high power devices below 2.8 GHz and above 4.5 GHz.