Had this issue a few weeks ago and here it is again.

Filr pointing to eDir.
Group syncing is enabled, as is scheduled sync.

Add a user to the group in iManager. Wait the 12 hours for Filr to sync.

Days later, users still aren't in the group

Run a manual sync, and it'll refresh the group.

What log files/where do I look at to determine:

a) Is Filr even running the scheduled sync (would be nice if the Admin Gui told you "last sync at BLAH")
b) If Sync is running, why is it not updating the group membership properly unless you MANUALLY run an LDAP sync (which takes a very long time, BTW, for some reason)