Every time that I try to create a number type variable, and then, I try to save, the editor tells me: “Unable to save as the project! Please try again by choosing another location!”. This only happens when I try doing that. Is it just me? 
This bug should have already been fixed in beta 110. The issue is that as you can see, the number field is empty instead of 0, an invalid value for number variables, so the project file would have gotten corrupted if you had saved and GDevelop therefore prevented that. On beta 110 it should detect empty values and set it to 0 if the value is empty/invalid.
I thought the same thing, so before posting this I tried to reinstall the beta 110 update, but, as you can see, to no avail. 
Well, I cannot replicate the bug on beta110, as soon as I convert the variable to a number it gets filled with a value.
nope, still gives me the error.
When creating one of those variables, a very big number pops up, but I delete it, maybe that’s the reason?? But I don’t think that GDevelop would fill the variable with such numbers on purpose.
Ah indeed it seems you can remove the number? That’s weird, I’m going to take a look