Have you appealed for the video? The system can make mistakes & in that case, an expert reviewer can manually update the monetization status. For future videos, please upload as unlisted & request a review, you can then publish once you get an email about the status.
Please appeal. This may happen because a video's classification may change after it's published as our systems continue to analyze more info from your video. We’re continuously working to make this process happen faster, thanks for sharing the feedback.