If a user has regular cycles for 2 years, then a late period, then the cycle resumes slightly offset, that could be a pretty solid hint. There are plenty of examples of women being arrested for miscarrying [1], which is more than enough reason to strongly advise anyone using a period tracking app to stop.
[1] https://www.bloomberg.com/news/articles/2022-07-05/miscarria... lists examples from Texas, California, Mississippi, Oklahoma, Nevada, and South Carolina