From https://www.drupal.org/node/438316 → , it states
Visit admin/settings/radioactivity, set Memcached entry expiration time to at least twice your cron interval.
And there is no such settings in 7.x-2.10, it turns out such setting was never landed in 7.x-2.x branch.
But, it indeed necessary for Memcache Storage, considering a very high traffic sites, the Memcache bins would be actively expired, which could loss on the incidents.
Closed: outdated
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Drupal 7 is no longer supported.
I don't know why the memcache integration was left out of the 8.x port, but if you would like to see it return please open a issue and hopefully contribute a patch, because the maintainers are not working on this.