Something isn’t right there. I’ve requested login details via your other post. I’m wondering if the same issue (e.g. a JavaScript error) is causing both problems. I’m happy to troubleshoot this for you.
Hey, I’ve just released version 4.7.5.2 which fixes this issue. It occurred when adding a new custom media query, as opposed to editing the existing ones. This slipped by me somehow. Many thanks for reporting it!