@mixology Looks like you would be having 2 Dynamo versions (1.3.4 and 2.0.x) installed for Revit 2018 & 2019. So the Batch Processor doesn’t know which version to open. I haven’t used Batch Processor so don’t know if you can define a default Dynamo version in settings or not. But my best guess would be to uninstall the version version you don’t need in 2018 & 2019.
EDIT:
Looks like this bug has been reported and a wontfix label has been applied to the issue. So not sure if there would be any other option but to try uninstalling one of the version!