Multiple people owning hardware with MT7613 have reported unstable behaviour on the 5 GHz radio (MT7613), resulting in the radio being still up but clients being unable to use the network. The issue is known and documented (GitHub issue #518) but no proper fix exists, except for a hack. Since it's no proper fix, it didn't make it into 21.02.
You can find the driver package including the hack here:
If you're not sure your device is affected, you can find a list of MT7613 devices supported by 21.02 below.
- I-O Data WN-DX1200GR
- Linksys E5600 v1
- TP-Link Archer A6 v3
- TP-Link Archer C6U
- TP-Link EAP235-Wall v1
In master there's also support for the TP-Link Archer C6 v3, but master is a moving target so you'll understand I am not providing packages for that.