If you read that wiki page and the links within it explains your questions.

I can only assume you have some how managed to install thumb without the errata workaround kernel.
If this is correct you will need to flash the device again to fix your boot loop issue.

There are currently three options...
Stable (for end-users)
Testing (for long term-testers and devs)
Thumb (thumb compiled version of testing)

If you are not sure please stick with CSSU Stable you can always upgrade in the future when you understand better.