I just realized I omitted the size change info from the strap. I’m forwarding my error to Craft, but in the meantime (bolded parentheticals were omitted):
[Under Strap#1]
Row 11 (13, 15): S1 1, K3 (4, 5), BO 3 st, K4 (5, 6) (so you’ll have a gap with 4 (5, 6) st on either side of it).
Row 12 (14, 16): Sl 1, K3 (4, 5), CO 3 st, K4 (5, 6).