We just spayed a 6 month old shar pei x Boston terrier. She was SO aggressive that we had to sedate her through the bars of her hospital cage. Owners are oblivious. "she is just scared."
Last year we had a litter of shar pei/pug x border collie pups. They're issues were not apparent when we saw them at 8 weeks but when we saw a few of them a month later for boosters, three had very serious and obvious (to me at least) aggression issues. One of the owners had two very small kids. I pulled her aside to tell her early intervention with a qualified behaviorist was essential or I felt confident the dog would bite someone. Owner unable to afford it, dog ended up being rehomed or surrendered after it bit her kid.
Enzo showed tendencies if DA when I had him that we immediately started working on m, and his current family is still working on with the knowledge that it may never disappear.