Did you do a factory reset after the update?.. I had this happen to me a while back with Oreo & found a factory reset after a major update takes care of the problem...it did for me anyways.
Hello , I have Galaxy S8 and running oreo that's before pie and my Samsung internet browser had updated and now my phone is doing the same as yours. It dont look like pie doing your problem I think it's the Samsung internet browser cuz mine is lagging and freezing and making my phone heat up and sucking power. I think go back to backup in your online and restore apps not all your other data just apps that may fix this. I would do it but the wifi here will take me 2 days to do restore