I now reverted settings in the opposite order: first enabled AP isolation and set no encryption on bridge and then on AP. Interestingly, AP changed the channel from 112 to 124 and bridge did not...

Disabled AP Isolation and set WPA2 key with AES encryption on main AP at 23:11:22 and bridge at 23:13:15. Bridge did re-connect almost immediately after I applied/saved the config; exactly at...

Maybe later at night. It's in use and we need open access to this AP during the day. Meanwhile, my bridge CPE did re-connect to the main AP automatically after another reboot of the main AP, but no...

Works for me. But you have to set up the SMTP server correctly. The CPE needs plain authentication (or none at all, but beware of bogus HELO message then) and it can not use TLS encrypted mail...

Hm, works flawlessly this time. This is what I have done: Set static IP, system time, bridge mode. Leave AP enabled, turned AP isolation on. Did a survey, locked to AP. Connected on first attempt...

Yes, but note that for the tests in #6 I had differing WiFi settings. I had AP isolation enabled on main AP and disabled on the bridge's AP. Then I disabled everything (even the bridge's AP at all)...