This is weird.

The past two days, sometime around 5:30 p.m. our GWIA stops processing mail. By stops processing I mean nothing comes in or out of it, yet the GWIA NLM screen looks fine (little twirly thingy), no errors. MTA is up and running on same server as well.

Nothing shows up in the log files (GWIA or MTA) other than they both "stop" showing anything at say, 5:30 p.m.

I don't see anything obvious like can't write to disk, etc.

Stopping/starting the cluster resource makes things work.

GW 8.0.1 (MTA and GWIA)
on NW 6.5.7 with post patches
In an NCS 1.8 cluster.