I have the identical issue to this post RStudio .Rproj.user conflicts with Dropbox which is now locked:
I have a number of RStudio projects stored in Dropbox folders on several computers. I know about the problem with .Rproj.user, and always make sure that I turn off sync of this folder in Dropbox: Using Dropbox with RStudio Projects – RStudio Support
However, recently, this no longer works. I get multiple folders .Rproj.user (Selective Sync Confilct 1) ...
Any idea how I can prevent this?