I have other games and they upload without problems. Only Scanner Sombre always upload until 80% them fails.
Anyone have this problem besides me?

Hello TaxAkla!

I do not have any experience with Galaxy and its cloud saves, nor how it manages them.
But have you considered the actual size of the save file from "Scanner Sombre"?

In my case each of the save files amounted to almost 1 GB in size at the end! (Installed from the offline installer the saves were stored within windows' app data directory, if you want to have a look.)

Maybe your cloud storage for Galaxy cloud saves ist limited and it does exceed when trying to upload your "Scanner Sombre" save or something with your connection and file integrity during upload, since it is all in one file per save state.

Otherwise, you could get in touch with GOG's support team.
Good luck and enjoy the game!

Kind regards,
foxgog

Actually my saves folder are just 309MB. I'll report GOG about it.

Same, Galaxy don't agree the saves as they are told too heavy.