Hi Filippo,
Well the warning just says the file is larger than 600MB and just to remind users (if it's not gzipped) to gzip.
It doesn't check if the file is gzipped already.
It's sets to 600MB maximum to now fill server storage.
Could you try removing some columns that FUMA doesn't use?
By removing some columns you should be able to reduce the file size.
Best,
Kyoko