This is what i see (znc.in/self-message script is disabled, only echo-message enabled).
<- @time=2022-05-05T18:11:08.887Z :znc.in BATCH -83dd4d95b9f42d9c44f500141edee67a
<- @time=2022-05-05T18:11:08.887Z :znc.in BATCH +b6a01e952006cea0db51db2fd0fa512c znc.in/playback normalnick
<- @batch=b6a01e952006cea0db51db2fd0fa512c;time=2022-05-05T18:10:12.071Z :zncnick!znc@IP PRIVMSG normalnick :dskjhjdf
<- @batch=b6a01e952006cea0db51db2fd0fa512c;time=2022-05-05T18:10:13.046Z :zncnick!znc@IP PRIVMSG normalnick :fdjhgdjfhgdf
<- @batch=b6a01e952006cea0db51db2fd0fa512c;time=2022-05-05T18:10:16.171Z :normalnick!hexip@unknownnetwork-a.clients.kiwiirc.com PRIVMSG zncnick :gflkjhgfk
<- @batch=b6a01e952006cea0db51db2fd0fa512c;time=2022-05-05T18:10:17.204Z :normalnick!hexip@unknownnetwork-a.clients.kiwiirc.com PRIVMSG zncnick :dfglkjdklgjfd
<- @batch=b6a01e952006cea0db51db2fd0fa512c;time=2022-05-05T18:10:18.151Z :zncnick!znc@IP PRIVMSG normalnick :dflkgjhdfkjg
<- @time=2022-05-05T18:11:08.887Z :znc.in BATCH -b6a01e952006cea0db51db2fd0fa512c
Still, echo-message was designed by the IRCv3 team as a replacement for znc.in/self message, there is absolutely no point to integrate it for everyone if they don't even use a ZNC + buffer. This is the one option that absolutely has to be optional with something like a box in the Server tab saying "Use echo-message when available." The delay is caused by the server response in ms, it may not be noticeable if the server is very close but there is a delay, in decades of IRC I never had to double check if a msg was delivered.
