Stone_Swan wrote:
yet you may not notice it
I'd notice it, you can be certain of that. Some of these actions are precisely to control file size in relation to pixel dimensions, for online delivery.
But just to be certain I did one direct save as jpeg, and one recorded as an action to produce the same size and the same quality level. They came out absolutely identical in file size (798 kB at 2460 x 1583, quality 8). This was a fairly detail-rich original, so that size is fully as expected.
The point I'm trying to make is that there's nothing in Photoshop's action recording that would cause this. There's something specifically wrong in your action steps, and that's why you should throw the whole action out and make a completely new one from scratch. If it still happens, it must be a corrupt preferences file.