Another suggestion: if you're not seeing any pattern matches, you might also want to test your patterns against spaCy's tokenization to ensure that they match as expected. If your patterns don't actually match and you're doing a textcat.teach cold start with a new category, your model likely won't learn anything meaningful, and Prodigy will keep suggesting you very random examples. This still doesn't explain the behaviour to describe – but it can easily make the whole thing more confusing.
We've actually just released an experimental tool that should help with testing patterns: