File Status diff is comparing against random old versions for changed files

To be clear the following issue makes SourceTree 2.0 completely unusable. I will be downgrading back to 1.9 until it is resolved.

After upgrading to SourceTree 2.0.20.1, I get a consistent problem where the SourceTree File Status tab randomly shows local change diffs against some random old version of the file (instead of against the most recent version). This leads to completely misleading diffs that don't reflect the actual changes that have been made.

If I bring up an external Diff of the file it is also against the wrong version, so clearly SourceTree is choosing the incorrect version at a low level somewhere. Stranger still, if I restart SourceTree often it will start showing the diff correctly.... only to then break again as I browse around on other changed files in the File Status UI.

I had never seen this in any version of SouceTree prior to 2.0. It literally started happening the instant I upgraded from 1.9 to 2.0.