Yesterday afternoon some time.
Strange, I only see two errors for any of your IPs over the last two weeks, both of
which are some bug in Sendy (see below, heavily redacted for security).
error.log-20170420.gz:2017/04/19 15:07:21 [error] 24952#0: *59443517 FastCGI sent in stderr: "PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at redacted) in redacted on line redacted" while reading upstream, client: redacted, server: redacted, request: "GET redacted HTTP/1.1", upstream: "fastcgi://unix:redacted", host: "redacted", referrer: "redacted"
error.log-20170421.gz:2017/04/20 19:32:25 [error] 24953#0: *62660078 FastCGI sent in stderr: "PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at redacted) in redacted: eval()'d code on line redacted" while reading upstream, client: redacted, server: redacted, request: "GET redacted HTTP/1.1", upstream: "fastcgi://unix:redacted", host: "redacted", referrer: "redacted"
Both of which are just header warnings, neither of which would have thrown a 502 error.