The 3 fails (14%) likely failed to recognize this BK is entirely surrounded and therefore cannot move. It behoves W to put him in check, in 3 moves, w/o moving the Knights. That leaves Bishop. Getting B over there is as simple as 1, 2, 3:
This time, after 1. Bb3, the robot 🤖 replied 1...c5 (opening the a4-e8 diagonal). I played 2. a5, then 3. Ba4#, so my success was undeterred after all.
1. c5...h3
2. Bb3...h2
3. Bf7#