Hi there.
Currently unable to add a workflow step in the website - using Google Chrome Version 66.0.3359.139 (Official Build) (64-bit) on Windows.
See video recording:
https://www.screencast.com/t/eqApcpa6o0t
It seems to work fine from my mac using Safari.
Issue seems to be identical to Unable to add a step
For now my workaround is to add steps from my mac.