Candidate's receiving an "Invalid Email" notification

Content

We have had multiple instances of our candidate's receiving notifcation that their email address is "invalid" as they try to apply for a job.  The message comes up mainly whne they click the "save and continue" option after completing the first page of the app and prevents them from moving on.  Each time I investigate it appears their email address is in the correct format and in several cases their profile gets saved as an anonymous submission.  We are on version 13a6.  Is this happening to anyone else, and any advice on how to fix it?  I haven't been able