That wasn’t it but your answer helped me find the problem: Pro doesn’t work with Firefox latest version (61). It works with Chrome and Safari (both worked fine once I realized you must be on a different browser) but there’s something wrong when I use Firefox. You might want to tell your developers, I doubt I am the only customer using Firefox. In the meantime I can do development with Chrome or Safari, so I should be OK. Thank you!
If it helps, I have no (zero) Firefox extensions or add-ons, and I’m on 61.0.1 (64-bit). I have all the Firefox security preferences set relatively private, maybe that’s the conflict.