inconsistency between @@global.gtid_executed and mysql.gtid_executed
mysql.gtid_executed is an internal table used to support some specific use cases; it's not meant to be monitored/used like @@global.gtid_executed (and other ways to access it, such as performance_schema.global_variables).

And it's only updated at certain times, which is what you were seeing. You can read more about it here.