Salesforce -> Smartsheet Connector Error (Notifications could not be reset)

Reporting an issue that has become a total blocker for our team. The Smartsheet Salesforce connector was working without issue for years and recently became completely stuck due to the following errors:

"We've detected a problem receiving notifications from SALESFORCE. Please press the “Reset” button to try to reset the notifications. As part of resetting the notifications, the rows in the sheet will be overwritten to be consistent with salesforce. Status reported from Salesforce: Unexpected error occurred. argument "content" is null"

"Resetting the notifications failed. Please contact your SALESFORCE System Administrator and let them know that notifications from Webhooks are no longer working so that they can investigate."

Has anyone experienced something similar? If so, what was the fix?