I had a go defining as a name either whole columns, a range in a column, or single cells. I then tried each in conditional formatting, with and without single quotes. I got confusing results. Mostly nothing happened. Sometimes formatting was applied - most often this was if previous conditional formatting had "hungover" from a previous attempt. I did not have time to pin down what was going on.
When I said:
The nearest issue I can see is
28589, although it isn't quite the same. I also think that one has been fixed in more recent releases.
I was remembering conditional formatting not showing until a cell had scrolled off and back on the screen, which occured in certain circumstances (more than one condition, at least one of which based on another cell). I know this problem has been resolved because it no longer affects me daily, as it used to.