In the last couple of days I have had similar warning message twice, to the below when trying to use PyRevit to copy over View Templates/Legends from one Model to another. The below is from trying to copy a Legend.
When I got a similar message when attempting a View Template, I shut down and rebooted Revit, tried again and it worked as it normally would. … But that’s when I noticed that the Settings/Filters etc, from the View Template in the original file that I was copying over had changed. Is this a knows issue for others?