If you haven't done anything, someone else might have. Check your router logs for strange devices and activity in your network, also check your machine/s for malware.
In our teams, is less about bugs and more about the team culture. A test mindset that ranges from the business ideas, to the new features developed and the code that we write.
We enforce 100% test coverage. Not 90, not 95, not 99, but 100. You need to test your code if you want to reach production. And production is the only environment we have. Having just prod generates less friction and allows us to make more changes, more features. But in order to live by this premise, the team needs to be really good at testing.
Have you explored the similarity between users? Recommendations are based on similar people. I usually use the user comparison view to check if I can trust the other user.
The user comparison view also shows you what the other user has seen and you haven't. Great once you trust the user to discover new movies.