Missing Shallow Tactics

Leela Chess is known to miss relatively shallow tactics in relation to the high level of play. The below is a rough draft explaining how the search works and why it misses shallow tactics.

Qxh7+ -> 2 (V: 31.72%) (N: 0.34%) PV: Qxh7+ Kxh7 hxg6+

The "2" means it searched Qxh7+ twice. First it evaluated Qxh7+, then it evaluated Qxh7+ Kxh7. But the PV shown is always one move deeper than the network has evaluated, so it hasn't evaluated Qxh7+ Kxh7 hxg6#. The extra last move in the PV just shows what the highest probability next move is.

Even when it does evaluate that move, it will score 100%, but that will be averaged in with the previous 32.72% score (1*1 + 0.3172*2)/3 = 54.48%).

See also leela search methods