MySQL replication with 5.7 master and 5.5 slave
From the source files, sql/log_event.h, event 34:

ANONYMOUS_GTID_LOG_EVENT= 34,


GTID wasn't introduced until 5.6, so there's no possible way a 5.5 server can understand this event (nor can the the version of mysqlbinlog that shipped with 5.5 understand it -- hence the error; you will probably be able to read this relay log if you use the version of mysqlbinlog that ships with 5.7).

It might seem like you could disable gtid_mode on the master, but there are two problems with this:


Even if that seems to work, it's completely unsupported, and only a matter of time until something else breaks.  The 5.7 master can emit events the pre-5.7 slave can't handle.


  when upgrading to MySQL 5.7, the slaves must be MySQL 5.7 before you can upgrade the master to 5.7. &mdash; https://dev.mysql.com/doc/refman/5.7/en/replication-upgrade.html

Any events written to the master's binlog since the upgrade are lost, from the perspective of a pre-5.7 slave, since such a server can't replicate them, so changing gtid_mode now is the equivalent of closing the barn door after the horses have escaped.  This slave's data is no longer useful, unless it is upgrade to understand the master's events and can continue replicating where it stopped.


You may still be able to salvage the slave if you upgrade it to 5.7 but I see no other meaningful alternatives.