I received an email digest for a group on our new community (which has been live for two weeks) and it was missing a lot of content. It only showed a handful of instances of new media, but not a single instance of forum posts, new users, etc.
I have not heard of our customers reporting this issue, because only a handful are subscribed. In the Event Log, only two others received an email digest. Interestingly enough, other users were subscribed, but the Event Log indicated the email digest was skipped because no content to report (for same group).
If you are still experiencing the issue, have you had a look at your SMTP logs for an indication of what is going on? Typically they are located at "C:\Windows\System32\LogFiles" on the server where your job service is running. There may be more information contained in the logs regarding the issue.