Table mysql/innodb_index_stats has length mismatch in the column name table_name. Please run mysql_upgrade

In mysqld.log I have thousands of lines like:

Table mysql/innodb_index_stats has length mismatch in the column name table_name.  Please run mysql_upgrade

So, according to virtually every post on the matter (and error msg itself):

mysql_upgrade -u root -p

Enter password: 
Checking if update is needed.
Checking server version.
Running queries to upgrade MySQL server.
Checking system database.
...

and all tables in all databases are like

```
...
mysql.columns_priv OK
mysql.db OK
mysql.engine_cost OK
mysql.event OK
mysql.func OK
mysql.general_log OK
mysql.gtid_executed OK
mysql.help_category OK
mysql.help_keyword OK
mysql.help_relation OK
mysql.help_topic OK
mysql.innodb_index_stats OK
mysql.innodb_table_stats OK
mysql.ndb_binlog_index OK
mysql.plugin OK
mysql.proc OK
mysql.procs_priv OK
mysql.proxies_priv OK
mysql.server_cost OK
mysql.servers OK
mysql.slave_master_info OK
mysql.slave_relay_log_info OK
mysql.slave_worker_info OK
mysql.slow_log OK
mysql.tables_priv OK
mysql.time_zone OK
mysql.time_zone_leap_second OK
mysql.time_zone_name OK
mysql.time_zone_t

Maybe this information is useful.

https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-23.html

Note

This release includes a change to the innodb_index_stats and innodb_table_stats system tables. When upgrading to this release, be sure to run mysql_upgrade in order to include these changes.

StackExchange Database Administrators Q#228203, answer score: 13