Yes, I tried both firmwares. The mesh works fine as long as any one of the following conditions is true (OR conjunction):
- OpenWRT 21.02.2 or earlier
- Non-DFS channel
- Non-ETSI domain
I need to use a DFS channel because the dedicated backlink radio of the AP only supports channels 100+. The non-DFS channels in that range have a very low TX power limit (which works, but results in a much worse SNR/lower bandwidth). Besides, no one uses channel 108 and I have had no problem with actual radar interference here.
Also, on principle, it is a regression in a bugfix release and I'd have thought at least the change causing it should be easy to pinpoint.