iCal invitation via email with RSVP button and no ics

When my wife invites me to an iCal event from her iPad Pro, I receive an email on my MacBook Pro that contains RSVP buttons, but no ics file to add to my calendar. At the top of the email there is a gray bar, which contains the event title and the RSVP buttons, Maybe/Decline/Accept. When I click "Accept" the event is not added to my iCal.

Does anyone know how to correct this problem, so that her iCal invitation email to me contains the ics? Or, a discussion thread that contains a solution?

This change is recent. Once upon a time, she could invite me to an event and I would receive an email with an event that I could add to my iCal. Then, have the option to select Maybe/Decline/Accept. And her event changes would auto update the accepted event on my iCal.

Thank you!

OSX Yosemite 10.10.5

MacBook Pro (15" mid 2009)

2.66 GHz Intel Core 2 Duo

8 GB 1067 MHz DDR3

1 TB SSD

Mail version 8.2