There are places where the ground swells and shrinks over the year depending on moisture content and/or freezing.
Freezing ground with lots of moisture in it causes swelling. I think it’s called frost swell – or something like that.
Another ground condition that causes seasonal rising and falling is a high clay content. Apparently clay swells when it’s wet and shrinks when it dries.
Huston, TX is famous for seasonal ground rising and falling due to moisture content. I understand the ground in Huston can rise and then fall at least a FOOT depending on moisture content. And this goes for buildings, parking lots, and single-dwelling houses. And weight means nothing. If the ground wants to swell and rise – 100,000 lbs. of concrete is nothing.
And here in Southern California we have earth quakes – which moves the ground up, down, and even sideways. After a really big quake, some of the guys in my club with permanent piers have to re-adjust P.A.
So there are several possible causes of PA changing.