It's all the new DragonMint B52 Blake2b miners being "tested". Personally I don't believe this burn-in/testing phase.
I think the coins used to test your products should be returned back to the customers. Or they should test in a separate environment.
It's not fair that we order the items, they "test them" for months, destroy the difficulty and profits, and then hand them over. I feel like should be illegal in some way.