All depends on the circumstances. Some have lost their status due to investigation of fraudulent agents, while others loose it for failing to declare relevant information that resulted in a successful application that would have been rejected if the information was included. Two things to keep in mind:
- IRCC does not pirouette revocation of permanent residence or, in particular, citizenship unless there are significant grounds to do so
- There is no limitation on when misrepresentation. If an application has misrepresented themselves, IRCC can pursue that at any time in the future.