Recently I had to investigate some Drupal website crashing. While debugging I noticed a lot of mysql crashes and MySQL log was full of errors like this:
InnoDB: Error: Column last_update in table "mysql"."innodb_table_stats" is INT UNSIGNED NOT NULL but should be BINARY(4) NOT NULL (type mismatch)
After some searching I managed to fix it by running mysql_upgrade command:
mysql_upgrade -u root -p <mysql_root_pass>
I added -p because my root username has a password, you can try without it first.