Alerts not sending to groups

Good morning, 

 I am encountering an issue with SharePoint alerts and groups.  Looking through previous threads I have already confirmed that the groups are defined as security groups as well as distribution groups, groups have read permissions to the list and site, and alerts are being sent/received by individual users.  There are also no restrictions on who can send to the groups.

What would be the next areas to examine, or are there any insights to a potential root cause?