Seems like a strange one. Windows 10 with Chrome one the first machine I tried it on. I wasn’t able to reproduce the fault at home. But I could with Ubuntu and Firefox, and Windows 10 with Firefox, though it seems if you move the items around a bit it comes back. I think the issue is that you don’t get a horizontal scroll bar if it extends out vertically. Here is the info you requested. Also another snap as proof.
It’s an oddball, as I mentioned now if I move the items around it does refit the slider bar eventually and you can resize it. As always if you need anymore info, I’m always happy to help.