That would be either:
1. The questions you're answering are getting taken down due to the community guidelines.
2. If you ask questions frequently, however many points you set for the reward for an answer is how many points you will lose. (yes, they can do that, and they do for whatever reason.)
For example: if you ask a question for 10 points, that's how many get revoked from your account.
hope this helps ^^