I've received a spam with U+061C ARABIC LETTER MARK characters in
the subject, which makes the index garbled in GNU Screen. I don't
know what they are, but they should probably be filtered out. This
can be tested on the attached mailbox, e.g.
screen mutt -F /dev/null -f mscreen-202205.mbox
The status line is 2 lines above the correct position.
When such a message is in a real mailbox, the index is garbled,
though if one doesn't pay attention, the index may look fine and
there is a risk to delete wrong messages, because some index lines
are shifted compared to the cursor (so, one thinks that one deletes
some message, but it is actually another message that is deleted).