Fix Error "Failed to fetch" in Customer Portal

There seems to be an issue where if an email message is attached to a work order, or perhaps if an attachment is corrupted, it makes it so you cannot update any comments on the work order in the customer portal.

I have attempted to update a comment on WO 1610643 through the customer portal but cannot and receive the attached error message "Failed to fetch". I have reloaded the page, logged out and back in and still am unable to process an update.