Added the URL filtering license(128 APs) to unleashed and it worked. However, new/existing APs cannot join/rejoin the unleashed network any more with error "Connection request from AP is refused;AP limit reached in URL Filtering license" until URL filtering was disabled on WLANs.
I used fixed 5G channels for my R710s and disabled all DFS channels. When using channelFly, the speed cannot match my unifi AC-HD and nanoHD. 5G range is short so your neighbours' signal is much weaker than yours; channelFly is not necessary.
Bought one from the seller and there are still a few.