K50 - first shot long exposure

Whenever I turn on my K50, the first shot seems to take several seconds, I focus, take the shot, the mirror comes up, viewfinder darkens as it stops down but then the mirror stays up for up to 5 seconds. After that every subsequent shot is fine. I also have the flash indicator in the viewfinder flashing.

Anyone know why the first shot (which is typically overexposed too) doesn't work?
Lens is a 55-300 HD-DA WR

If the mirror is up the viewfinder should be completely blacked out. The lens stopping down should not be noticeable. Can you try another lens on the camera and the lens on another camera to eliminate one ?

Tried with a different lens, same issue - when first turned on - shot taken, viewfinder dark (appeciate the mirror likely down), lighting in viewfinder (flash charge?) flashes then 1-5 seconds later aperture opens up again.

Never owned a K50 so cannot advise I am afraid. They can suffer from "Aperture block failure" which may be related to your problem.

I've had this periodically on the K-3 too, but on a K-50 I'd definitely be thinking aperture motor failure first, but pay to check with other lenses too first.