Show stars Mandy Moore and Milo Ventimiglia are bickering on the set of This is Us and their frosty vibes are throwing the cast and crew into a panic, RadarOnline.com is reporting. “This has happened with Milo on every hit show he’s ever been on,” snitches the source of Ventimiglia, who is notorious for keeping his personal life private.

“From Gilmore Girls to Heroes — the show gets successful, then Milo gets self conscious, and he starts withdrawing from the camaraderie of the crew, the producers and his fellow actors on a show!” The introverted star is said to get “melancholy and not cheerful,” which sources claims take a toll on his co-star Moore.

“Mandy loves the job but the roller-coaster with Milo can be a little too much.”

“He walks around with his earbuds in all day or with his head buried in a book. That’s fine for a guest star but Milo is the leading man, the first guy cast for the show, and at this point he has more experience than a lot of the people on the set.” And for Moore — she may just be reaching her breaking point.

“Between their emotional scenes on camera and the unpredictability of his disposition when they aren’t shooting,” — it weighs heavily on the actress.