We have just bought an E400 and got it installed about a month ago. Before that, our vendor was kind enough to loan us a test unit for a month and it worked very well.
The new unit that we bought so far has caused connectivity issues for 2 times within a month time. All clients were not able to connect to the wireless network out of sudden until we got to reboot the device. The log (as attached) shows clients being disconnected immediately after it connected to the AP. The E400 is configured with 2 wireless network, 1 for 5Ghz and the other for 2.4Ghz.
I faced this problem with some of smartphones. It seems that there is some problem with Band steering, because everything is fine since I turned Band steering off. It worth a shot, I suppose, try it if after update AP would not be able to connect users.
If you require bandsteer, then 2.4G clients take more time to connect or multiple retries required for connection.
Otherwise you can disable bandsteer and clients will connect to AP smoothly.
Yeah, I know how it works, but band steering realization is different from vendor to vendor, and with Cambium I often see that 2.4G clients simply could not connect to SSID with Band steering — last time I tested it on first version of Autopilot. Client activity was very similar to opening post — legit CONNECTED and DISCONNECTED events with no time in between. When I turned off Band steering, problem was solved, so if it had worked for me — maybe it will be useful for someone else :)