So based on my first experience on the V19.07 branch of the mt76 git repo.
The two routers using this driver, would keep disconnecting client with this message, if the country code is other than 'World' setting.
Your assumption is probably correct and that the world settings satisfy the frequencies it needs. There was so much broken functionality on this V19.07 branch, i switched to the 'compat' branch then backported recent fixes.
From then on i no longer had this issue. There was so many missing patches in the V19.07 branch, i just used the compat in the end.
I'm in the process of porting across the mtwifi drivers, these are drivers from a chinese git repo, they seem to compatible with the V19.07 branch. Only issue is they have their own luci interface for changing wireless control.
But i just wanted to see how good the drivers are.