One of my friends keeps getting booted out of my realm

One of my realm memebers keeps getting booted out or it won't let him join. He gets kicked out within 5 minutes when it does let him in

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
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Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
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