racking the slide after a reload
I believe that the H&K Academy did/does teach to manually cycle the slide after any reload, to make sure that a round is chambered.
One of the reasons they do that is commonality of doctrine through the entire H&K weapons group, because their long guns DO NOT lock open after the last round has been fired. I don't know why that is. I have an H&K 91 and have a little trigger time with the MP5 series guns, and I always thought that was a significant design flaw.
(It is possible under stress to short circuit an out-of-battery/slide lock reload by hitting the slide release BEFORE the magazine is in all the way, thus chambering empty air and creating a failure-to-fire malfunction. I've seen inexperienced shooters pushing for speed make this mistake.
Some schools teach the solution to that issue is to use the thumb of the SUPPORT hand to release the slide AFTER that hand has inserted a fresh magazine.)
But racking the slide after a tac reload done behind cover during a break in the action? Well, I suppose that's one way to be CERTAIN that there is a round in the chamber.
If you have long thumbs and shoot with the currently popular thumbs forward shooting grip, it is possible to ride the slide stop and prevent the gun from locking open when the last round is fired. In such a circumstance, you may believe that you are doing an in-battery reload when in fact the chamber is empty, and manually cycling the slide guarantees that there is a round in the chamber.
There are so many weird nuances of weapon manipulation possible, and you don't want to overthink this stuff and suffer from paralysis through analysis. Pick a manual of arms that works for you and your weapons system, and stick with it.
If you get training from a school affiliated with a particular manufacturer, remember that some of the techniques they teach will be specific to THAT particular variety of weapon, and those techniques may NOT be appropriate for some other weapons systems.
There is not one true answer. There are many answers. You just have to make sure to ask the right question