https://youtu.be/P0GIn96p4Gw shows the bug in a video. A user reported:

Make the choice parameter hidden i.e. let the panel have a scroll bar which has the parameters, then go to the choice parameter in my case it is test is named testchoices and try to expand it you won’t be able to find it. In order to do that Just go to Run through blueocean, don’t run the browser in full screen mode, try to expand the list that won’t happen.