Baryon number violation, one of the requirements for baryon asymmetry, only occurs at any significant rate in the Standard Model at high temperatures, much higher than are known to exist in the universe.
We know experimentally that any other processes that violate baryon number must be quite rare and/or occur only in extreme conditions, since we have not yet observed any.
Theoretically, black holes violate baryon number conservation. Black holes don't have a baryon number, and so when a baryon falls into a black hole, its baryon number is lost. If you consider a neutron star collapsing into a black hole and what happens afterwards, its pretty easy to convince yourself that baryon number can't possibly be conserved.