Mark -- The following bug was recently reported by a user in GMF ( https://groups.io/g/Group_Help/message/1870 ).
If you require hashtags in the group and an incoming email does not meet those criteria, the message is held as a Draft until that person logs in and corrects the subject line. But if the message is also supposed to be moderated, it does not go into moderation after being fixed, nor does it bypass moderation and post. It simply disappears.
This occurs whether the message originated from a regular Member or an Owner. I've confirmed this with the following settings:
Spam Control > Message Moderation > All messages are moderated
Message Policies > Hashtags Required
Message Policies > Hashtag Permissions > Messages from members can only be tagged with existing hashtags, otherwise the message is bounced
I suspect that some other obscure combinations of settings could lead to the same behavior.