Node count goes down when multipv + per-pv-stats is on.

[mooskagh]

During the WCCC testing, there were several cases where number of nodes for a particular variation went down as time went.
I tried to reproduce this by analyzing same positions in freshly started Lc0, but it was not reproducible.

There are three legal moves in this position, and nodes graph looks like this (move above is green line)

Another example:

Lc0 version
master as of 2022-07-19

Lc0 parameters
--multipv=20 --per-pv-stats

Will attach logs later today (if not forget).