I have a simple workflow that is "failing to start - retrying".

It is a email notification attached to a Sharepoint List.

I cannot find anything wrong with it. The user who created it stated that it started failing back in May of this year, but just reached out to us now to ask about it. When I looked at it, the only thing that looked suspicious to me, is the # of entries for "email addresses" in the "to" field.  Other than that, it's a very basic email notification.

When I asked the user about it, she did tell me that they added two more email addresses around the time that the workflow started to error out.

Is there a limitation set on that "to" field somehow?  I can't test the form since it's live and will notify all the groups in that list, but I'm hoping she will be able to remove a few of the email addresses and test on her own to let me know. In the meantime, I thought I would come here to ask to see if that may be the cause.

No other problems with Nintex on our farm, no other complaints of failed starts, etc.