I've recently upgraded all my AP's to HiveOS 6.1r1.1247, one of them is working fine, but the other one keeps disconnecting from my hive portal. The AP is functioning as I can connect to it and browse the network
or go to monitor and select AP then click utilities and get tech data and have a peak through those logs.
also consider doing a complete config upload and reboot
I remember that since I block all DNS other then opendns, I had to change the default DNS settings which pointed to aerohive DNS servers. So for me a clean AP would load then I pushed config and then it would disappear from the hive and autoreboot every 15 minutes trying to revert to previous config in order to reach the hive.