Emails in Email Groups disappear on iPhone 11

All of a sudden when I try to send an email on my iPhone 11 to an established group, the group has no emails in it. The group is fine on my iMac- has all the email addresses in that group, and I can send a group email on my iMac with no problem. This is true FOR ALL of my groups when I try to send a group email on my iPhone. The group pops up on my iPhone with the message "No Members." Help!