Hi Ed,
Our team got this one figured out for Eleza, but whatever you're running into may still be unresolved?
Can you take a screenshot of the version and file size of this dll: ArcGIS.Desktop.Docking.Wpf.dll ?
If you left the default install location, it should be located in C:\Program Files\ArcGIS\Pro\bin
Find it there, right-click > Properties and then click on the Details tab. Mine looks like this:

1. Please send a screenshot of yours.
2. Also, you had 2.1.x installed before upgrading. How did you upgrade? Did you use the auto-updater from within ArcGIS Pro, download and install from My Esri, other (Explain)?
Thanks!