Viewport height issue after completing oAuth flow in PWA

I'm building a PWA in iOS Safari and use Facebook and Google oAuth to authenticate my users. When the oAuth process starts, the user is taken to an external link and the nav bar on the bottom of the page reappears, changing the viewport height. When the auth process is complete and the user is returned to the PWA, the viewport height is the same as it was during the oAuth process (when the bottom nav bar was visible) with a white space about the same height as the bottom nav bar where the bottom nav bar used to be. This white space persists even when I visit new pages within the PWA. Rotating the device and rotating it back removes the white space until I log out and go through the oAuth flow again. This happens on the iPhone 8 and 11 using iOS 13.5 in the Xcode simulator as well as my iPhone 7 using iOS 13.5.1.

Any thoughts or help anyone can provide would be much appreciated.