It's probably a missing path or permissions issue. Are there any messages in the console (~ key) when the save fails?
EDIT: I'll try it on my VM later, but I'm probably using a different flavour of Linux so I may or may not be able to reproduce the issue.
EDIT 2: It's a bug on my end, I used the wrong path separator somewhere.
EDIT 3: I figured it out and there is a hotfixed post-jam build. It almost certainly affects the macOS build as well but I haven't built/tested that one yet.