Microsoft installed a few stupid filename-overrides into windows to "help" users with wrong filenames.
Unfortunately that means that those overrides hide errors you made with your filenames, and those errors usually appear as soon as you move to a non-windows platform where the filenames are expected to be correctly used instead of redirected to allow the OS to load the wrong file if the filename is similiar.
Capitalisation is one of the possibe causes (only windows sees no difference between A.png and a.png, to all other OS that are two different files), but there are others as well.