WKWebView video rendering slows to a stop

I am using a WKWebView with an embedded YouTube player. Alongside this in my app, I am using WhirlyGlobe - an OpenGL based 3D globe library. Rendering of the video in the web view slows until it comes to a stop. I had not experienced this when using UIWebView. Rendering performance picks back up when I tap the fullscreen button in the video controls or use picutre-in-picture.