AKC GSD came up Mixed breed on Embark Test - Page 1

So I have what I thought was a Purebred Czech German shepherd dog. I had bought him at 7 weeks old from a breeder, whom gave me his AKC registration, parents on site, along with his litter mates. 
I gave him an Embark Test for health purposes, & it came back that he was not a purebred GSD, he was 87% German Shepherd & 13% Belgian Malionis. 

 

How would I go about his AKC paper work... do I let AKC know they have dogs (from this lineage) that are not pure but are registering as pure with papers? 
Also how does something like this happen? When both parents were Sable German Shepherds & had the papers to show it?

Another question, is it true say if a female purebred GSD gets mounted by another male dog who is not purebred GSD, BUT she does not get pregnant by this male but he did get inside her, then she now Carrie's the DNA from that male & she will pass that mixed males DNA down to her litters, even if she was mated with a Purebred GSD & it was a successful pregnancy. 

You should DEFINITELY let AKC know about this! That breeder is going to be in big trouble with them! Dogs registered with AKC are supposed to be pure bred.

Imported sires must be DNA tested if they are going to be used for breeding. This SHOULD have been spotted previously, as you said the pup is from Czech lines.

Since the pup is only 13% malinois, the mal parent must be 2 generations back.

A female being mated by another breed of dog has absolutely NO influence on future litters. What can happen is if she's in heat and gets mated by both a GSD and another breed of dog, some of the pups may have that dog as a sire, and not the GSD. The genes will NOT mix, though - pups will get half their genes from their mother, and the other half from the non-GSD sire. The other pups in the litter will be pure GSD.

Was this dog originally imported from Europe? Possibly Germany with RSV 2000 papers?

Embark is not accepted on the PDB for health testing of dogs unless it is verified by OFA .  Members have sent in results on Health Testing to the OFA to find the tests were wrong on HD, ED, DM, etc. Dogs that were tested with other USA labs proved to be unrealiable to develop these diseases.  DNA Testing of a dog to prove sire and dam can prove if a dog is a Purebred GSD.

DNA testing for a dog breed is not proven to be accurate at this time. 

DNA testing kits for dogs are super popular. But the testing has some veterinarians pushing standards

https://www.usatoday.com/story/news/nation/2019/03/08/dog-dna-testing-test-kits-popular-but-veterinarians-warn-risks/3065059002/

@Sunsliver Thank you! I have already been in contact with AKC letting them know.

Embark is the worst...did a mixed breed and came up with the craziest results...none of which we trust

Inclined to agree with Stacy about Embark and all the other "We will tell you which breeds are in your dog's history." 'tests' - most have a poor reputation for accurracy. Too many stories of these only being in the game for the money they make. They are meaningless in terms of pure-breed Registers, which AFAIK only accept the entirely separate sort of DNA testing that confirms if your dog is the offspring of the parents shown on its pedigree papers.