Sydney Sweeney’s new flick “Christy” didn’t exactly light up the box office this weekend … and one model tells TMZ it’s ‘cause the actress kept her clothes on this time.

We spoke with Ella Halikas, who told us “Christy” shows a side of Sydney fans aren’t used to seeing … so seeing her throw punches instead of seducing the camera might’ve thrown everyone off.

Ella elaborated … saying the “Euphoria” star is famous for showing skin and embracing her bombshell vibe, so with her all covered up, audiences probably didn’t know what to make of it … and that’s why they skipped the movie altogether.

Of course, Sydney’s still shaking off that viral jeans ad backlash from the summer … and clothes or not, it looks like some of that heat followed her to the box office.