Hi Jan,
In case the grib file is damaged in some way, can you use 'grib_ls' or 'grib_dump' to check the entire file can be read, e.g.
grib_dump ICMGGgvfc+000008
it will produce a lot of output but will confirm the file can be read ok. I suspect the file is fine but good to check.
When using cdo, it is best to split the file so that each level type (pressure, surface) is in a separate file. Cdo's cgribex engine doesn't tend to work well if it sees a mix of vertical coordinates. You can do the split like this using cdo or grib_api depending on your preference:
# cdo solution cdo splitzaxis ICMGGgvfc+000008 ICMGGgvfc+000008_split # grib_api solution. grib_copy ICMGGgvfc+000008 ICMSHg4a4+000000_[typeOfLevel]
Then try again.
There are, unfortunately, a few caveats when using cdo with OpenIFS grib output, particularly when converting to a regular lat-long grid.
I recommend reading both this page on the OpenIFS website: How to convert GRIB to netCDF (including comments at the bottom) and this post on the OpenIFS forum: Grib to netcdf conversion, which goes into the caveats and workarounds in much more detail.
Regards, Glenn