About Chandler and Monica?

So I have this question about Chandler and Monica, and perhaps it’s already been answered here, though I haven’t find any discussion about it, or mentioned on the show and I haven’t paid attention. If so, please excuse me!
But why does Chandler act like he doesn’t know that Monica was overweight in season 2. Because in season 2, when Monica unboxes her high school stuff, and Phoebe finds out about her high school swimsuit or when they watch the prom tapes, Chandler mocks Monica about her weight as if he didn’t know she was overweight, when he clearly did in the later seasons.

Is it just a show’s discontinuity?