@rhibbert Thank you for this post, it helps my sanity.
Using Studio 2020.4.2 the exact same thing occurred when I incidentally entered an ImplementationVersion on my workflow as I was writing Test processes.
I too do not have the knowledge of the use of the ImplementationVersion property. But ouch, didn’t think it would cause this situation. Resolution was to leave it blank in all circumstances.
Definitely would like to find out what that property is supposed to do.