cr1cr1: Same issue here: the GOG Galaxy client from GFN seems to be an older version and GOG servers probably broke API compatibility. This is something you do not do in software :)
The end result is that game save are not synced, with an misleading message that the ... cloud service is busy.
Contacted GFN Support to at least get manually the savegames, but... I would not hold my breath around that.
Unfortunately, there is no way to hack around this, not unlike using the embedded Steam browser and upload your saves to a cloud drive
GFN's lack of GOG integration makes it easy to "claim" a game on a platform and - if without issue in itself - run a machine under the platform that's different from the OP's local machine. I could imagine that the saves themselves could be a mismatch of the version used in a save, even if used on the same copy of the game. That is, a platform might generate a different version of a save. However, the OP failed to specify, leaving much room in the imagination to speculate.
I don't have the game personally, and frankly no GOG game on GFN to verify any of this. But knowing the particulars of how GFN handles saves which also has the ability to save locally only in the GFN cloud, I could only imagine there's something that's different with the game/platofrm itself, rather than there being a difference in the Galaxy client. if it's going to the GOG cloud, there shouldn't be an issue with putting it on the cloud itself. That is, unless the OP clarifies they are using GFN in the same condition as their local machine.
EDIT: Are those saves not accessible through Galaxy itself? They should be, especially with concern about the cloud purging happening tomorrow. You don't need to refer to GFN's help if the saves are directly on GOG's cloud.