Just by loading one page and coming back, we can't make out the memory leak. Try multiple times like this. If you see a increase & no decrease then we can conclude memory leak. If you can send me the complete example, we can try as well.
@GrecKo I found that it is a bug that is affecting all platforms with certain screen resolutions. Some developers may not notice this issue but the end user may be using a certain screen resolution and be affected by the issue! You can login to https://bugreports.qt.io/ and Vote THIS bug if you also want this bug to be resolved.