Exported Bottom Mesh Is Incomplete In Blender

As shown in the image below, the entire section of the waistband is missing in the export. I have set my settings up to the proper Blender.exe file and am using version 2.79. I also tried it with version 2.76 as that is the latest most compatible version noted on the forum, but it shows up the same as whatever version I use - 2.76, 2.79, and even 4.0. 

Any help would be greatly appreciated, thank you!