That's actually a very common problem with the protege models. The needles and loopers must be threaded in the proper order and any variation will give you a breaking lower looper thread. From the BabyLock customer service FAQ page:
Q: I have the Protege serger and my lower looper thread keeps breaking. What is wrong?
A: Whenever the lower looper thread breaks, unthread the "eye" of the needles. Then re-thread the lower looper. The needle thread wraps around the lower looper and whenever you re-thread the looper you enclose the needle thread and the needle thread then breaks the lower looper thread.
found here:
http://babylock.com/support/FAQ/?FAQ=10 Double check the machine's manual for any additional threading tips. If you don't have a manual then contact the Babylock website for a replacement:
http://babylock.com/
If that doesn't help then take the machine in for a servicing. It sounds like there might be something wrong with the tension discs especially if you are using one setting and getting an unexpected result. It's possible a spring might have popped or snapped, or it's possible vibrations have made a screw tighten or loosen. A service check and tune-up might be a good idea.
For a bit more on troubleshooting a serger here's a video sponsored by BabyLock:
https://www.youtube.com/watch?v=RqPgA_P1m5A with a link to a site that offers even more help for BabyLock users.