File syncing issues 
There are generally a few causes of slow or stalled file sharing. Here are some workarounds and checks you can do in each circumstance.
1. Has my sync stalled or failed? 
A common reason for a failed sync is that the docker filesharing daemon has crashed. You can resolve the latter by restarting the docker daemon itself.
2. Is my app located in a shared directory? 
Your app needs to live inside of a shared drive or folder. Here are the following default shared drive/folder locations:
| OS | Shared Drives/Folders | 
|---|---|
Windows | C:\ | 
macOS | /Users, /Volumes, /tmp, /private | 
Linux | All the folders | 
Note that on macOS these need to be HARD LINKS. In other words, you cannot symlink /Users to /SomethingElse and expect it to work. This is often the case if you have an external drive.
Also note that you can add additional folders and shares to Windows/macOS through the Docker GUI.