When copying repositories back and forth between Windows and Linux/MacOS, you may end up either with core.ignoreCase=false on Windows or core.ignoreCase=true on Linux. Both configurations will usually cause troubles and are not supported by Git [1].
To avoid this, you may unset the core.ignoreCase configuration in your repository root:
$ git config --unset core.ignoreCase
As Git’s internal default is false, there is nothing more to do on Linux/MacOS. On Windows, you have to add core.ignoreCase=true as global default:
$ git config --global core.ignoreCase true
[1] https://git-scm.com/docs/git-config#Documentation/git-config.txt-coreignoreCase