Question about rules for puzzle classification

[karol-brejna-i]

I have a pgn file that contains a set of 2-movers (forced mate in 2).

Yet, make_puzzle.py is not qualifying them as valid puzzle candidates.

Take a look at the following problem:

python3 make_puzzles.py --threads 16 --memory 4096 --fen "B7/8/8/8/3k4/2p5/2KP3Q/8 w - - 0 1"

The solution is: 1.Qc7 cxd2 2.Qc3#

But make_puzzle.py produces "Puzzle incomplete".
See output (edited):

Stockfish 2020-06-13 64 BMI2 Multi-Variant
B7/8/8/8/3k4/2p5/2KP3Q/8 w - - 0 1

Evaluating best initial move (depth 22)...
  1.     Qc7 (h2c7)     Mate: 2

After 1. Qc7
B7/2Q5/8/8/3k4/2p5/2KP4/8 b - - 1 1

Material difference:  12
# legal moves:        1
Evaluating best move (depth 22)...
  1...   cxd2 (c3d2)    Mate: 1
Going deeper... not player move

After 1... cxd2
B7/2Q5/8/8/3k4/8/2Kp4/8 w - - 0 2

Material difference:  12
# legal moves:        33
Evaluating best move (depth 22)...
  2.     Qc3# (c7c3)    Mate: 1
Evaluating best 3 moves (depth 22)...
  2.     Qc3# (c7c3)    Mate: 1
  2.     Qa5 (c7a5)     Mate: 4
  2.     Kd1 (c2d1)     Mate: 5
Not going deeper: ambiguous
Puzzle incomplete

Could you explain the criteria that are considered?