One pernicious problem I had with tinydns and EDNS support was in an environment where one firewall, for whatever reason, did not permit tcp/53. So DNS replies

One pernicious problem I had with tinydns and EDNS support was in an environment where one firewall, for whatever reason, did not permit tcp/53. So DNS replies worked, EDNS0 replies worked, but not from certain clients that insisted on retrying the query over TCP. Needless to say, after tons of time getting into the weeds with EDNS, and STILL not understanding why certain clients weren't working, that was a fun one to solve.