I just attempted to upgrade BalenaOS on one of my Raspberry Pi 3 devices from Resin OS 2.15.1+rev2 to balenaOS2.29.2+rev2 and I was seeing a 502 Bad Gateway error. In order to get the device working again, I had to log into my switch and manually power-cycle the port to get the Raspberry Pi to reboot. This is a hard reset and not good for microSD cards. Anyone know why this would have happened?
A couple of questions to understand better your situation.
During the update process your board came offline and it was not getting online anymore until you manually power cycled it?
After manually power cycling the board the board had the new OS release or still the old one?
When the upgrade ran, it did reboot, but never booted to the new OS. I saw a 502 Bad Gateway error. I logged into my switch and turned PoE off and on again to reboot the Pi (I am remote to this location). Then it booted to the new OS. It seems to be running well now.