Hi,
For the last week NOAA has been experiencing problems with their made FTP service for several models including GFS.
In the last 48 hours the service has stopped completely. There is an option to download GFS for the NOMADS Grib Filter but this requires a completely different setup of the data preparation scripts.
Until the problem is resolved - I suggest using ICON as an alternate global data source. This is working in XyGrib without any problems.
David