Hypoglycemia w/o diabetes. Diet not helping.

Hey y'all.. So I posted before about my hubs. He was always a sugar drinker ie soda/monster. Few yrs back he noticed he felt like crap after drinking a soda. We bought a bs machine & his sugar was high 200 range. Switched to zero sugar drinks & life went back to normal. Recently he started having 'episodes', a little while after eating his eyes would get wonky, persistent headaches, awful night sweats, & vision changes. He noticed his bs was dropping into the 40s with some of these. He went to the VA and they did a bunch of BW, ALL of it came back normal! A1C normal, glucose normal, thyroid normal. It doesn't make sense! We've switched his diet to a protein complex carb diet after posting on here and getting feedback for reactive hypoglycemia. His BS when waking up is usually in normal range. He's eating lots of small meals through the day that have both a complex carb and protein and his bs is still dipping low. He is not overweight, 6'1 180. He doesn't drink alcohol, doesn't do drugs and is on no medication for anything. Since he's not diabetic I'm worried it could be something worse like an insulinoma. Does anyone else have hypoglycemia without diabetes? There has to be an underlying cause, right? If diet is not helping, what do they do next? He's 40 and we have 4 small kids. This has been terrifying for us. When his sugar drops low he feels like he's in a fog all day even after he brings it back up. He builds homes for a living and feels like he's becoming a liability to his boss. His pcp is referring him to endocrinologist, but not sure what to expect. Thanks for your help!