E9.1 Suddenly R3483 generating no records to F3411


Hey all, what am I missing?

Today our R3483 MRP batches are producing no records in the F3411 file, for any items in any of our branches. The jobs complete in a minute when they normally take about 45 minutes, and no records are generated.

I've checked processing options, data selections, shop floor calendar, re-generated work center resources just to be sure they are there, all to no avail.
Check to see if the report wasn't accidentally set to read only!! It happens especially if someone's in there updating the flag using sql