For me:

I specifically created a new Function App Plan in Azure to upload an old function to, to test the performance between plans. Every deployment showed success from VSCode however the function name never showed up in the overview like this is what I was expecting. Even the files blade showed that they had been uploaded.

This is different from all the other answers because in my case nothing was actually wrong with any of the code and nothing needed to be changed.

Steps I took to solve:

1. in VSCode use command to "Create a Function" and choose to add an HTTP trigger to your existing file.
2. Delete the new trigger (you can only have one)
3. Add a space to make sure the file is "new"
4. Save
5. Upload as normal to your function app.
6. After success a pop up will show in VSCode with a button to "upload settings". Click that which will fire another upload.
7. Wait about 2 minutes and refresh the function app in Azure.

This is what I had to do to make them show up for me. I am not sure if step 6 to upload settings was necessary but it's what I did.