When GTID_NEXT is set to a GTID, you must explicitly set it again after a COMMIT or ROLLBACK. If you see this error message in the slave SQL thread, it means that a table in the current transaction is transactional on the master and non-transactional on the slave. In a client connection, it means that you executed SET GTID_NEXT before a transaction and forgot to set GTID_NEXT to a different identifier or to 'AUTOMATIC' after COMMIT or ROLLBACK. Current GTID_NEXT is '%s'
Information specific to MariaDB SkySQL can be found on the ER_GTID_NEXT_TYPE_UNDEFINED_GROUP page in the SkySQL Documentation.