Have you tested thoroughly? After adding something on your Android device - did you sync that device before syncing the windows app etc?
I use Joplin on four devices and have no problems at all. For example I can add “Note A” from Android, “Note B” from my iPad, “Note C” from Ubuntu 18.04 and “Note D” from Windows 10. After all devices have been synced a couple of times - all notes appear fine on all devices.
There seems to be an issue in the Joplin/Dropbox/Linux combo so I had to set my devices up like this:
- Windows 10 > Syncs via Dropbox API
- Android app > Syncs via Dropbox API
- iPad > Syncs via Dropbox API
- Ubuntu 18.04 > Syncs via Filesystem ( Directory: /home/username/Dropbox/Apps/Joplin
Ubuntu syncing via Dropbox API did not work, but with filesystem it syncs very fast.