The problem sounds like it is related to insufficient or uneven drying based on my experience. Another concern is that a print somewhat damp from sensitizing may transfer the sensitizer to the negative and ruin it. Thin sheets of mylar can prevent that if sandwiched between the negative and print.
I've always had better results double-coating. Also, a 20% silver nitrate solution seems to work better than a 12% solution. Salt prints need an excess of silver and the stronger solution ensures that.