This morning (GMT-4) I downloaded a NOAA OAA OPC NCOM US East (current) file that Expedition could not use. It is described in the Grib Folder as a NC file. I downloaded it through Exp My Grib and it appeared to download as it always has in the past.

This was not a showstopper here as I substituted a RTOFS download at a hi-res setting for the currents that I needed but I am interested to know if anyone can advise whether this was a one-time server anomaly or a change in the NCOM product.

Thanks    

Just guessing:
Maybe boat 5 is mapped as an AIS target?   Then you receive just aan AIS 'ping' from that boat as it is in your vicinity, but not enough data to actually bring meaningful data into your log file (SOG, COG).