A directory full of files for Drush commands for versions of Drush before 9 still exists. They are no longer needed, since this version of key does not support versions of Drush older than 10.
Remove the directory of obsolete files for Drush commands.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I'd suggest dropping Drush 8 support independently if the maintainers want to drop support for Drupal 8 or not. No one should be using Drush 8 with Drupal 8.
Most users of Drupal 8 should probably be using Drush 10, so that the system can run on PHP 7. I don't think any hosting providers are still allowing PHP 5.6.