turns out i actually had a similar issue, at different server, years ago,

https://pagure.io/pagure/issue/4983

per comments there, checking @

https://pagure.io/pgnd/dkimpy-milter-UPSTREAM-MIRROR/settings#mirrorlog-tab

nothing's been logged,

Mirrorring in log

Here below is the log of the last attempt to mirror in this project.

  None

The service seems to have died, but I am not fully sure why.

There are tracebacks/errors from mirroring something that doesn't exist, but that doesn't seem to have caused the service to stop.

I restarted it, so that might bring things back, but might be a short while as it mirrors all the configured mirror repos.

the mirrror's indeed now populated. thanks!

is the 'mirror service' that was down also responsible for pulling updates on change from the upstream?
is there a end-user probe/notification of if mirroring/updating isn't functioning?

Yes, the same service is the one that pulls all changes into mirrored repos

There isn't any end-user way to tell. In fact the service appeared to be running but was 'stuck' and not logging anything. ;(

So, this may need some upstream work to detect this better... will see if it happens any again.