I think there is some shar-pei in the mix as well as mastiff.

I don't really think shar-pei - they are not the type of breed that there are a lot of "accidental" litters born
Here are some dogs are a rescue near us - they are siblings and here is the listing

Wrinkles and Megan are 5 month old, 35 pound Yellow Lab/Shar-Pei mixed dogs that is looking for a new home.




This same rescue group has had other shar-pei mixes too.