20w22a EXPERIMENTAL RENDERING CHANGES laggy/jittery

Put the summary of the bug you're having here

*What I expected to happen was...:*normal game play 

What actually happened was...:

jittery, laggy, unplayable; the previous snapshot worked fine. I have an older Radeon HD 4200 graphics card

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