Look at the words "I am not sure" in the editing window and in the preview in this image. In the editing window they come after the expression that is shown following them on the next line in the preview. That happens in this question.
Here it is after it is saved:
\;
(latex) command, was not working correctly, when imbedded re$abc \; def$
. I was never able to reliably reproduce the problem. When I posted on math.metaSE, someone suggested the~
command instead. I switched to that command, and it works. I suspect, but can not prove, that mathJax on mathSE does not like longer posts. I could easily be wrong. $\endgroup$ – user2661923 Oct 14 '20 at 1:02