Manuscript and journal submission author order differs?
Things happen. Online manuscript systems can be confusing and frustrating. If you are not paying attention, mistakes can be made. Assuming the PI did the submission, I would mention it to the them. Something along the lines of


  I noticed the order of authors is different between the title page and the submission form. I believe the title page of A, B, C is the correct order. If it is, we should make sure we fix the submission form before publication. If the order is now B, A, C, I would like to discuss the change.


I would do this in person and in a friendly manner. If B did the submission, things are messier, but I would still mention it to the PI directly. If C did the submission, you can email them directly noting the discrepancy.