The Flow and PowerApps Move tasks/functions will assign a new Message ID whenever an email message is moved from one Outlook folder to another. If you store the Message ID when an email arrives in folder A, you can use that Message ID to move that email to folder B. You cannot use that Message ID to subsequently access that email. For example, you cannot move the email from folder B to folder C because Flow assigned a new Message ID when the email moved to folder B hence breaking the reference to the originally stored Message ID value.
It would be useful to track an email with a constant Message ID (i.e., that is not dependent on the current folder location). In the alternative, an overloaded Move() method which returns the new Message ID after a move would help resolve the issue of tracking emails when they are moved with Flow or PowerApps.