Submitting webform with version 3.15 throws an error. version 3.11 submits successfully

[AndrewBowne]

I have an instance where I want to open(edit) an existing survey record but do not want to make any changes.  Effectively, I just want to re-trigger a webhook.  When I do this with the webform at version 3.15, it throws an error:  "Failed to submit. - 500 unable to complete operation". 

 I checked the log files an the only error that is thrown is, "An error occured".  

If I publish the same survey with version 3.11 I am able to resubmit a survey without making any edits. 

I am also finding that webhooks sometimes are triggered and sometimes are not.  I search of the forums reveals that I am not the only one with this issue.

Any thoughts why the most current version won't submit an unedited webform?