Today I came across on the same issue.
In my case the problem was about applying position: fixed to element by shadcn Drawer package. When I opened the bottom drawer, that library updates position of the body and only in iOS PWA the bottom bar together with drawer content has been shifted.
Screenshot:
I've managed to fix it by adding height on the root HTML element:
html {
min-height: calc(100% + env(safe-area-inset-top));
}
How it look after: