Known for generating massive gains for investors, Chipotle and Cava Group have seen their stocks fall mightily to 52-week lows following their lackluster Q2 results.

The trend isn't universal. Denny's Corp. (DENN) has been feeling the pinch from the promo deluge. Still, last week, it pointed to signs of firming demand and said its own "Buy One Get One Slam for $1" ...

Fast-casual players are seeing a decline in same-store sales, or smaller growth, compared to this time last year.