6k1/8/1pK4p/bP6/1p6/8/P1B2P2/8 w - - 0 5

[Matthies]

Rubi fails to find winning move Bb3. The null move criteria may are bad. phase < 255 may not be enough, mobility should also be checked.

[Matthies]

Origin of the problem is this position: 4K1k1/8/1p5p/1Pp3b1/8/1P3P2/P1B2P2/8 w - - 0 1
Best known line from here:
1.f4 Lxf4 2.Kd7 Ld2 3.Kc6 La5 4.b4 cxb4 5.Lb3+ Kg7 6.Kd5 Kf6 7.Ke4 h5 8.Kf4 Kg6 9.Ke5 h4 10.Kf4 Kh5 11.f3 h3 12.Kg3 h2 13.Kxh2 Kg6 14.Kh3 Kf5 15.Kg3 Ke5 16.f4+ Kf5 17.Kf3 Kf6 18.Ke4 Ke7 19.Ke5 Ke8 20.f5 Kd7 21.f6 Ke8 22.f7+ Ke7 23.Kf5 Kf8 24.Ke6 Kg7 25.Ke7 Kg6 26.f8D Kg5 27.Dd8 Kf5 28.Dc7

[Matthies]

Release version 2.0 finds f4 immedialtely with > +3 but switches to drawing move Kd7 later at depth 37 with > +4. Later at depth 45 Kd7 decreases to ~ +3 switches to Bd1 at depth 50, back to Kd7 and so on.
Well, I close this.