[anabab]

What if it has some sort of a booster to increase its kinetic energy just before the hit?

Also the behavior might improve in an area already weakened by a ventilation shaft/previous hit (first bomb turns 40 meters into fine gravel + detonates weakening quite a large are, second and third bomb easily go deeper)

[maxglute]

I think 1) is unlikely, b2 bays can't fit much more, gbu57 is mostly metal and no booster for penetration 2) is what no one knows, but we (as in the public) also don't know layout/construction, i.e. actual depth, bunker design (can emb sloped concrete/steel layer to deflect penetrators laterally so follow up drop don't go straight down).