It will be useful to add such info as connection_id that attachment owned before abnormaly ends connection and server writes to firebird.log record with 104 or similar info.
some_host Mon Nov 12 03:42:13 2018
INET/inet_error: read errno = 104, client address = 172.17.56.34/59821, user = john_smith.4294967295.4294967295
-- does contain IP address but it is almost useless when multiple connections are established from the same IP.
Also, i can't understand for what reason FB log contains time with percision of seconds rather than ms. Is it possible to increase time precision there ?