I can believe that Tandem - I have had 2 endoscopies, one normal, one not, and my symptoms were identical even when things were normal to look at. I have food allergies but have been told my acid reflux is unrelated.
A hernia can also be visible on the scope. If you have one planned, make sure they test for coeliac disease and Helicobacter at the same time.
New stuff: GERD. Interstitial Cystitis
Lifelong stuff: Food allergies, eczema, asthma