I use same SSIDs on my network, too.
Sometimes, when an AP is down, the CPE will connect to another AP it can reach with considerable low signal strength. But this is better than no internet at all.
I wonder if one could write a script that does the following on the CPE-device:
1) If the registration is not from the main-AP (checked by MAC-Adress of the AP it is connected to),
then drop the connection after one hour of connection-uptime. Afterward let the CPE reconnect again.
2) If the registration is bound to the correct AP, then simply let it run and do nothing
This will ensure, that the wireless registration will move to the correct AP, when it is available again.
Otherwis it will have reconnects on a one hour schedule on the 'wrong' AP.