Realm won't let me replace or play existing games with mods

Put the summary of the bug you're having here

What I expected to happen was...: I should have been able to replace my previous realm game with a new one
Describe what you thought should happen here

What actually happened was...: it wouldn't import my new game
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. I requested to play game on realm.
3. I picked my current realm game to replaced with new world 

4) tried to load and said unexpected error. I have mods that I'd like to play on my realm but it won't let me