Could be, I’m not sure. Did it change the fade rate when you physically press the switch on the wall?
If so, then, yeah, maybe it’s not working that way for network commands.
Have you tried asking in the webcore forum to see if anyone has another way to do it?
https://community.smartthings.com/t/introducing-the-new-webcore-community-forum/96259?source_topic_id=59981