Version
4.7.0
Reproduction link
https://jsfiddle.net/758vs6xe/
Steps to reproduce
You have an xAxis of type category and you have a bar series. And you want to markArea of a specific category. You can't because the markArea starts drawing from the center of the bar.
In the example we have the days of the week as categories.
With markArea 'Mon' - 'Tue' you see something.
With markArea 'Wed' - 'Wed' you see nothing.

What is expected?
For markArea to mark the specific bar category.
What is actually happening?
It doesn't mark it.