Something is wrong in TWX. Here is the bottom left of the Composer:
"Waiting for available socket"
I wanted to post a screenshot, but it seems I am no longer able to.
This looked like a bug, but no: actually this is a user error. I have another tab showing the TWX Runtime, and it currently has the login dialog up waiting for my password. When I login correctly in that tab, then my Composer works fine.
So this is not a bug, but it is a usability issue.