Yeah when Lang bought thermite, stashed it in his house, and then got irritated because it all went bad it was some real CB comms. He started hiding it in his house people the Manor stash was a mess and he hated when his stuff got yoinked. Mickey kept asking for thermite from him but Lang was so busy and tired he didn't often want to give it unless he was doing the job with Mickey, but he doesn't like new Fleecas, and Mickey liked to do slightly degen Fleecas so the boys don't have to. So Mickey didn't want to harass Lang over the thermite he knew he had, and I don't think Ray or Yuno ever really knew.
Basically, moral of the story, Mickey organizing the Manor stash has brought salvation. I don't think anyone was ever trying to steal, the place was just a nightmare inventory shared by a billion people with zero organization.