The salesforce_mapping_object_delete_form() was patched to be picky about its first non-form argument ($entity) in https://www.drupal.org/node/2883966 → . This causes an error when attempting to delete mappings from the "Salesforce Activity" tab of a mapped entity.
3.0
salesforce_mapping.module
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.