CDO

The same problem with these GFS files:
https://www.nco.ncep.noaa.gov/pmb/products/gfs/

Any function of CDO does not work!

Here is the output of grib_ls:

GFS_grib2_2019090300_003.grib2
edition      centre       date         dataType     gridType     stepRange    typeOfLevel  level        shortName    packingType  
2            kwbc         20190903     fc           regular_ll   3            surface      0            t            grid_simple 
2            kwbc         20190903     fc           regular_ll   3            heightAboveGround  2            2t           grid_simple 
2            kwbc         20190903     fc           regular_ll   3            heightAboveGround  2            2r           grid_simple 
2            kwbc         20190903     fc           regular_ll   3            heightAboveGround  10           10u          grid_simple 
2            kwbc         20190903     fc           regular_ll   3            heightAboveGround  10           10v          grid_simple 
2            kwbc         20190903     fc           regular_ll   0-3          surface      0            tp           grid_simple 
2            kwbc         20190903     fc           regular_ll   0-3          surface      0            tp           grid_simple 
2            kwbc         20190903     fc           regular_ll   3            unknown      0            r            grid_simple 
2            kwbc         20190903     fc           regular_ll   0-3          surface      0            dswrf        grid_simple 
2            kwbc         20190903     fc           regular_ll   3            meanSea      0            prmsl        grid_simple 
10 of 10 messages in GFS_grib2_2019090300_003.grib2

Records 6 and 7 are identical. This is not supported in CDO. Each time step must contain different variables. You must remove one of the double variables so that CDO can process the file.
A workaround for this problem is to set the environment variable CDI_INVENTORY_MODE=time.
This will ignore double parameter entries on the same time step.
Here is an example for the shell sh/bash:

export CDI_INVENTORY_MODE=time
cdo ...

Dear Uwe,
thank you very much! Problem solved, it works fine!
I did not notice the double parameters using Panoply, but you can see them with grib_ls.

Cheers
Alessandro