I think this would have been happening since 2014 when the pop-up definition window was introduced. Probably people only started noticing it recently when they were switching between the two sites to try to get the forum summary to show.
Anyway it's fixed now, but you will definitely have to reload the Chi page, at both sites. Some mobile devices seem slow to reload scripts, even when the page is refreshed, so on such devices the problem may hang around for a while.
In case you're interested, the problem arose from my reuse of a script I'd written for the
Letterbox game. In that game if you're playing on a small screen such as a phone, information is presented as a new page, identified by a # extension of the address, rather than a pop-up panel, so dismissing the information acts like the browser's Back button.