They are living things. Anything can happen.
Pipping in the bottom area is not all that unusual. It is not normal, but it is not that unusual. It is not ideal, but many do that and survive OK. These are some of the possible causes.
Florida Incubation Troubleshooting
http://edis.ifas.ufl.edu/aa204
ac.Sign: Chicks malpositioned. Normal position after 19 days of incubation: embryo's long axis same as long axis of egg; head in large end of egg; head to the right and under right wing; beak toward air cell; feet toward head. Causes:
ad.
i.Eggs set small end up or in horizontal position.
ii.Inadequate or improper turning.
iii.High or low incubator temperature.
iv.High humidity.
v.Old breeders.
vi.Round-shaped eggs or very large eggs.
vii.Nutritional deficiencies, especially vitamin A and vitamin B12.
viii.Eggs handled or stored improperly.
ix.Retarded development.
x.Embryos <18 days old may be in a position different from that for hatching but one normal for their age (for example, the head-between-thighs position). The feet-over-head position is hard to distinguish and may be normal. The beak-over-wing position is probably a normal variant. Some malpositions are lethal; others are not.