Recently I encountered the following problem.
In my local git repository files have the names starting with Build*:
$ ls Build/
Build.data.unityweb Build.wasm.code.unityweb UnityLoader.js
Build.json Build.wasm.framework.unityweb
When I push master branch to heroku:
git push heroku master
and connect to see what's there
heroku run bash -a name-of-myapp
It shows that names start with BUILD*
~ $ ls Build
ls Build
BUILD.data.unityweb BUILD.wasm.code.unityweb UnityLoader.js
BUILD.json BUILD.wasm.framework.unityweb
And my app doesn't work because it looks for files with name Build*.
Additional info: I develop in Unity, Windows-platform. Then build an app in Unity to create WebGL app. Than deploy it to heroku. It worked, but have stopped working yesterday.