I bought this router yesterday and it worked fine.  The Admin Portal instructed me to upgrade firmware, so I did, to the latest version available.

Now the 5Ghz network barely works.  2.4Ghz is OK

Symptoms are:

1. High packetloss for connected devices (95% packetloss)
2. Any packets that do work, are high latency - eg up to 4000ms 
3. The same devices exhibit no issues when connected on 2.4Ghz
4. My previous router works fine in the same area on 5Ghz, proving there are no environmental or interference issues
5. The issue occurs after channel changes, Transmit power changes, and changing other settings eg MIMO
6. Devices usually cannot connect at all - with a report of "Bad password" even though the password is correct

The device has been factory reset to the beginning.  I am using the default factory wifi settings and the issue still exists.

Does anyone have any suggestions?