Omg has anyone had a problem with github and case-sensitivity? Had renamed my React component file names by capitalising the first letter - so from 'app.js' to 'App.js' etc. Worked fine when running locally but when I deployed to Heroku certain files couldn't be found. For example, in the code 'App.js' is referenced but I guess on Heroku 'app.js' was being looked for. Anyway.... I have fixed the problem by entirely renaming my component files. Deployment to Heroku is OK now. What a royal PITA.