Same issues buddy.
Are you using the default drivers for 5 Ghz?
Yes. Software and driver wise nothing has changed.
So I would follow @jdwl1o1's suggestion to reset and re-configure from scratch.
Or, downgrade to 19.07.8.
I did that at the time. Shall I reset the device again?
If you've already done a reset, and re-configured from scratch, it's not likely it will work a second time.
Your call.
I would downgrade to 19.07.8 (use the sysupgrade image), re-configure from scratch, and see if it works.
What do the syslog and kernel log say? I’d disable the non working radio, then re-enable and look at the log, see if the driver throws errors.
Edit: did some research, radio2 should be left disabled.
If it’s still bad a reflash could help. Do a sysupgrade and don’t keep any settings. Make certain the image matches your device.
Share a bootlog and kernel log from disable and enabling radio 0.