mysqldump select queries appearing in slow query log after upgrade
By default, MariaDB's mysqldump will log queries (--log-queries enabled by default) to the slow log when executing the reload of a dump. The MariaDB doc says:

When restoring the dump, the server will, if logging is turned on, log the queries to the general and slow query log. Defaults to on; use --skip-log-queries to disable. Added in MariaDB 10.1.1.

This was introduced back in MariaDB 10.1.1. You could try skip-log-queries as an option for mysqldump.
This may or may not affect the dump process itself.
If you are seeing SELECTs from the mysqldump in the slow log, the table being dumped might be waiting for a lock to release (in the case of a MyISAM table) or an table with a lot of transactional activity (in the case of InnoDB) when generating the INSERT INTO for thousands of rows.
SUGGESTION
You could initialize the reload session to ignore the slow query log by hiking the long_query_time for the local session:
mysql --init-command=&quot;SET long_query_time = 10000000;&quot; &lt; dump-file.sql