The special 'P' character used for papyrii in text critical discussions appears correctly in most places in this section of Porter on the iPad. However, as you can see in the screenshot, it is undisplayable in a few places - see the paragraph that begins "One objection."

If you look at the same location in L5, you can see that the actual character is different than the cases where it displays correctly on the iPad.

This is a variation of a typo, IMO. Worth reporting and fixing in all locations in this resource.
Thanks,
Donnie