Is this something to do with my method of opening files every time I start a new session. When I was working on the same desktop pc I’d simply open the project I wanted from the recent files dropdown on the welcome window. The filename stayed small. Now I’m alternating with a laptop and desktop pc and have to open existing project from my dropbox folder. I choose the most recently modified which has a bak2 or something attached, and each switch of machine grows the filename another bak.
The .bak files are Scrivener’s automatic backups. You don’t want to work from those: it’s nearly guaranteed to cause confusion, because every time you open one it will make an automatic backup, and so on indefinitely.
Automatic backups are stored in the location specified in the Scrivener -> Preferences -> Backups pane. The live project should be stored somewhere else.
Personally, if you’re going to use Dropbox to share the live project, I would recommend not using Dropbox for your automatic backups. Too many eggs in one basket.