WAC510 Firmware Version 9.9.0.10 "Firmware Upgrade server not reachable."

We have the same problem.  Updating two units from 9.6.0.12 (We reverted to old firmware because later updates caused bad behavior with our access points!).  We've had repeated issues upgrading firmware with these Netgear access points.  We made the mistake of thinking that by this point, with a 9.9.x version upgrade things might have been fixed.  

After firmware upgrade, when I click the button that says "Check for Updgrade" from the Dashboard, both units show the error message that the firmware upgrade server cannot be reached.

Last night, I upgraded 2 units.  The first appeared to upgrade fine.  The second one showed a message at reboot about there being a problem with the firmware update.  No further details.  That's when I tried to see if I could reflash the firmware by clicking the "Check for Upgrade" button again, but then saw the mentioned error message. 

The thing is, despite the error message, the second unit rebooted into the new firmware and is running the new version anyway.  WTF?  Why would it boot into a new firmware when it detects a problem upgrading to the new firmware?  Shouldn't it have booted into the backup firmware?  Or could the unit have updated the firmware fine, but the error is actually related to the issue of not being able to access the upgrade server, which is why it didn't boot into the backup firmware?  But if that were the case, why didn't we see the same error about a bad firmware upgrade with the other unit, since both units say they can't access the firmware upgrade server?

For the unit that did NOT show any error message after the firmware update, this morning, suddenly users couldn't access wifi via the access point.  Wifi was confirmed to be functional last night.  Suddenly saved Wifi passwords would not work to connect to the access point.  I had to manually reboot the WAC510 to restore wifi access.

Gotta say, with these repeated Netgear access point issues, they are not going to be deployed in our business for long.  We need reliability and stability, not spontaneous and repeated headaches...