Mention suggestion not added upon clicking it

I was trying to put a mention to duplicate monumentum , after typing a few characters, I get the suggestion list. But even when I click on the desired userName, there is no adding it to the content I am typing. The clicking stays irresponsive. ie, nothing happens even after I click on the mention suggestion.

If I try WoltLab , the same thing happens. So I guess it is global with all userNames.

Testing @GTB , no luck.

I see that those mentions got added in above post. Not sure if that is because I typed full userName. Let me try a half one Charly

No, Arian Glander and after clicking on suggestion, it is not imported to content.

WoltLab, test