Hello   @jbyers

To resolve this you can deleted the group provider from the K2].2HostServer].rGroupProvider] table and then delete the settings for the site from the hK2].2Integration].nProcessSharePointSetting] table.
After both are deleted and the K2Server restarted, all should be well again.

Additional Information...
When you remove the K2 App from a site collection, you keep the K2 related configurations in the DB still.
One might need to remove the K2 App for various reasons like when you want to make a template or copy an artifact from one SP farm to another.

If you removed the configuration information in the DB, your settings would have been lost and you probably had to re-create everything again. And if you recreate a smartobject, it will get created with a different GUID.
If that smartobject was used anywhere on a view, form or in a workflow, everything that uses that will be broken and this why you keep the info in the DB.

Should you find the above information useful kindly mark as "Accepted Solution and/or Kudo", as this will assist other community members looking for related information.

Regards,
BesM