Hello. Unlike the 1911, the HP's slide stop lever has constant downward pressure from a detent in the pin portion of the stop that meets a spring-loaded ball in the spring guide assembly. I've have never seen one of these go bad, but I reckon it could happen.
Try the following: With the HP empty and the magazine removed, push up on the slide stop lever when holding the slide back. The lever should pop back down when you release it.
If it doesn't do this, the detent is not engaging the spring-loaded ball. I've seen this happen when some have put the spring guide in upside down. Usually, however, the spring guide breaks with the first shot. There is usually a crack in the donut shaped area of the guide through which the slide stop lever pin passes. If this has occurred, you will need a new guide and they come with the spring-loaded system intact.
Otherwise, I suspect you may be bumping the lever with your off-hand some way.
Best and good luck.