Thank you for this incredibly useful and well written article.  I turned to it after struggling to get fast romaing working but I'm still having trouble.  My S21 phone comes into range of the seocnd router but invariable I get a "connection failed" or a "couldn't obtain IP from DHCP".  WHich is really odd as it shouldn't be trying to get a new IP at all.  I have one access point and one main router both running OPenwrt and bot with 2.4 and 5Gz bands all using the same SSID and password. 802.11r,v and k are all enables with BSS selected for the v protocol as advised.

The two routers are conected by LAN cable and both have the "mode" under geenral setupo set to "access point".  

Can you think of aything that might be going wrong?