Danny is a new technician at a rebuilt star labs. He didn't want to at first because Danny thought it would cut into his undead superhero/prince duties. Eventually though Clockwork (bullied) encouraged him and as it turns out, the lab is pretty lax about sudden "trouble at home". Plus, Danny can help set things back together when one of the Flashes messes up the timeline AGAIN.
(Flashpoint is what allowed Dan to come back as quickly as he did in the first place.)
The flash family, for lack of a better description, are straining. They're all putting up painted smiles that Danny knows aren't happening with his coworkers. Danny wants to be friendly with them but they're keeping him at a constant arms length away.
Barry, wally, Bart, and the rest of the flash family are freaking OUT. Why wouldn't they, their new technician caused the apocalypse. Granted they only know this because of an old speed scout from Bart. But it didn't have the time to tell them anymore than the name and some powers of one Dan phantom before fading. The timeline line the one man disaster's from doesn't exist anymore so they can't even check what happened or why the Dan destroyed everything. They can't even get rid of him because what if that sets off the guy!