Have you tried creating a very simple workflow with just send notification in just to see if emails are working at all? 

Hi Cassy .. emails are working.  I am getting the first email for 'Send Nominator Receipt' and I am getting the email requesting the confirmation (approval) from the Flexi Task.

Ok how is the send notification configured? Have you added yourself in "cc" to see if you get it? 

OK, so this is really embarrassing but as it turns out I had an outlook rule from a similar project I was doing over a year ago that was causing email from the return notification to be forwarded and deleted.  So I apologize .. <face palm>

I'm marking this as the correct answer because I added someone else from the AD list to the CC and they of course got the message.

Haha happens to the best of us - I had a very similar issue this week! ‌ haha