emacs dropped ctrl-x x in its newer versions, it seems - what a shame ! apparently I was the only user, for the last 15 years! So not even emacs is as holy as it used to be.
(NB - this post is intended as humorous, no more - yes, I use ctrl-x x and it's gone in some incarnations, but I did literally NO work to investigate why that might be! Could be completely trivial!)