Diagnosis
Yeah, this one's common. The 36" has four independent burners, but the center of the cooking surface is where the heat from the two middle burners overlaps, creating a hotter zone. The front edge is farthest from the burner tubes, which run front-to-back under the steel.
How to Fix It
First, make sure your propane tank isn't low and all burners are on high with a strong, blue flame. If they are, you just need to learn your griddle's heat map. Use an infrared thermometer. The center will often be 50-100°F hotter. Plan your cook: sear meats in the center, keep toast or buns near the front, use the rear for warming. It's a feature, not a bug—you get different temp zones.
If That Didn't Work
If the temperature disparity is extreme (one area not getting hot at all), a burner might be clogged or the orifice might be faulty. You'd need to check for an even flame pattern on each burner by looking underneath (with the griddle off and cool).
Heads Up
Preheating with all burners on high for 10-15 minutes is non-negotiable to let the massive steel slab equalize. Even then, the front edge will always be a cooler zone. Use it strategically.