We updated our server to GMS 2 a few weeks ago, some clients have been
upgraded, most others have not.

Since that upgrade, on occasion, generally lasting a while (maybe an
hour or more), most of our users (might be all, I'm not sure) quit
receiving all mail, appointments and PIM info on their devices. If you
look at the web interface, no new information is being displayed there

I look at the User Activity and everything looks normal aside from the
"no changes", which is wrong as there should be updated info. There are
no errors.

The Server Activity log shows little info, aside from "Mobile Gateway
unable to deliver message to Systems Management" which others seem to be
dismissing as a unknown "feature".

We are using:
GMS2 (our upgrade path was GMS1 -> DST Patch -> GMS2)
Secure Gateway
with about 100 users

I'm really not sure how to troubleshoot this issue. I'm really not sure
where to look. The POA isn't busy, the GMS server isn't busy, none of
the logs give any indication. . .

Any help would be greatly appreciated.