Put the summary of the bug you're having here
What I expected to happen was...:
I closed out of my world called Pre-1.11 because I was experiencing large lag spikes. When I went to reopen the World, I assumed it would load back in completely normal.
What actually happened was...:
When I tried to reopen my World, I would continuously crash my launcher.
Steps to Reproduce:
1. Open the Launcher
2. Run the Launcher
3. Open my Pre-1.11 World and let it load
4. Crashes
Related issues
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Comments

Please attach the crash report (.minecraft/crash-reports/crash-<DATE>-client.txt) here.
Please do not mark issues as private, unless your bug report is an exploit or contains information about your username or server.

Sorry about that.

I attached the crash report.
Thank you for your report!
However, this issue has been closed as a Duplicate of MC-12949.
Your Minecraft is out of memory. See this article on how to allocate more RAM.
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[Mod] Neko, if you need anything from my Pre-1.11 save, I have that too