infoboxes won’t drag

The pages is built using infoboxes on row layouts. New infoboxes are added periodically. Up until earlier today, I could drag infoboxes around to alphabetise the titles. Now none will drag and move, they just revert to their original position when the mouse is released.

I’ve used this for approach for several pages for several years. I was mid-session when this change happened and had already moved a bunch of infoboxes when it stopped working.

I’ve done all the obvious switch-it-off-and-on-again stuff, including the page, the browser, the machine and tried it on different browsers. All with no change.

Suggestions welcome.

The page I need help with: [log in to see the link]