Looks like db2.stats has some corrupt tables, looks like wp_versions and archival_wp_versions are affected.
This has caused WP version stats to cease to operate as expected: https://wordpress.org/about/stats/
I’ve put the stats scripts into maintenance mode to prevent it trying to write to these tables (while still processing autoupdate stats/etc), if I’m not around to do it myself, please execute UPDATE `rev2_ingestion_settings` SET `value` = '0' WHERE `key` = 'maintenance_mode'; afterwards to re-enable it, if possible.