iOS Mail - Not syncing between iPhone and iPad

I’ve noticed recently that when filing mail on the iOS mail app on my iPad, those changes are not accurately reflected when using the mail app on my iPhone - for example, I moved several emails from a Gmail account to a new Yahoo! Mail account folder on the iPad - those emails still remain in the Gmail inbox on my iPhone and the new folder is empty but for one moved email. I’ve deleted and re-added the Gmail account on the iPhone, but it still doesn’t sync the changes.

All mail is visible on both devices when it’s delivered and this is a new problem. Any idea as to what might have gone wrong?