@acommons and @izaychik63, I know it’s not ideal, but a temporary solution that worked for me was to downgrade to KNIME 3.6.2 and reinstall the RDKit extensions.
You can download previous versions here: https://www.knime.com/download-previous-versions
Also, If you grab the “self extracting archive” download for 3.6.2 and open up the application via the ‘.exe’ file, you’ll be able to keep it self contained for the time you are using it, so you don’t have to worry about removing your current KNIME installation. You may want to create a new workspace directory, however (I’m not sure if that really matters, but better to err on the safe side).
Hope that helps in the meantime.