Realms and Servers not working

On my Google Pixel 3 phone, I can never play Realms or on any Servers. "Use Cellular Data" is turned on. I have tried on a good Wi-Fi connection and with a good cellular data signal, and the only online feature that works is LAN. Usually when I click on one, it starts loading and gets to the "Loading Resources" screen, then tells me "Unable to Connect". On my tablet, a Samsung Galaxy Tab S, all of these features work on Wi-Fi (it doesn't have cellular data).