Every time I try to load in the new snapshot, the game crashes out immediately after the Mojang splash screen appears. Every. Time. I have tried everything I can think of: reinstalling Minecraft, reinstalling Java, even deleting the entire .minecraft folder and starting fresh, but I keep getting the same crash message:

Unable to bootstrap data fixers

java.lang.StackOverflowError

as well as 

Something went wrong updating!

java.lang.NumberFormatException: For input string: "25:SHIFT"

I'm attaching the launcher log as well.

Thanks for the assistance.