Thanks for the update. Do you have a callback URL configured? Where does it go?

Getting this same issue on CiviCRM 5.33.5 on Drupal 8.9.17. Occurs for any set of search results that has the action drop down... the dropdown is made active when one or more contacts are selected, but no action is exe Select2 is installed on Drupal, but even with it disabled no search action is available. (Noting that v8.x of Select2 does not provide for exclusion rules.)

On the reruns, were temp tables used? Where?

Check that the smart group is not corrupted. We have noted with recent upgrades that smart groups can get munged and need to be rebuilt. Be sure to refresh the smart group cache as well. (The Explain says that temporary was used for civicrm_group_contact_cache_5e8691eef0e92 so that's my guess.)

Jon... it looks like this was a problem before with regard to filtering on contact_id issues.civicrm.org/jira/browse/…). In this case, there are no filters and the error is occuring.

Again, it would be helpful to see the code. Also, is there anything in the CiviCRM log? A stack trace would be great if one is available.