require() / --@include not working for some files.

My issue goes like this:

I have a set of libraries in lib/ which are stringLib.txt and tableLib.txt
I have an a script in fun/ which requires lib/stringLib.txt
I also have a script in tools/ which requires both lib/stringLib.txt and lib/tableLib.txt

I am using --@include and require() as I'm supposed to.

For some reason, the script in tools/ is able to require both libraries, however the script in fun/ cannot require lib/stringLib.txt.