Why emails from Google Groups not getting to comcast

I belong to 3 groups that use Google Groups for emails. I suddenly stopped getting their emails in my Xfinity account about 3 weeks ago, and missed some deadlines. I have been on these groups for over 2 years with no issues. Then the emails stopped arriving. They are not in my Spam folder. I have no rules pertaining to their email. What can I do to start receiving their emails again?

Thanks