You should never work on an Atomic project inside a Dropbox, OneDrive, or other cloud storage folder.
Atomic projects are not single documents like Microsoft Word. A project contains a multitude of files for each scene and note, as well as a database to bind everything together. These files must be kept in synch with each other, otherwise you risk data loss and incorrect data apearing in your project.
Recognised issues with services like Dropbox incluide partial or incomplete synchs, multiple file creation, and more. All of which will have a negative effect on an Atomic project.
If you wish to work on your Atomic project on multiple PCs, you must copy the project in its entirety from on PC to another. Methods of doing this include USB or flash drives, network drives, emailing projects to yourself, or extracting zipped backups from a cloud folder (Dropbox will work for this.)
Again, NEVER open a project directly from a Dropbox folder.