Disconnected after a couple of seconds when connecting to multi-player servers

Whenever I connect to a multi-player server (including a realms server) I can play normally for about 10-30s before I get disconnected. "Disconnected from server" I am using mobile data, and I have even set up a firewall on my phone to block other apps from using data. I get this issue with full signal (4g lte). I don't have access to wifi to test that out. I have changed the battery optimization setting to off in the android system settings.