I don't believe there's a bug with safe-area-inset-bottom.

The issue is that a position: absolute div doesn't take up the whole viewport when the tab/url bar is floating above it.

Therefore when you do set safe-area-inset-bottom it shifts up the frame by the correct amount, but it's already effectively shifted up since it wasn't filling the viewport in the first place.

Enable safe-area-inset-bottom