Man, I sure feel for your frustration. Kind of another data point to think about: you felt better when you consumed more protein when you rode. Perhaps this was not so much a result of more protein as it was a result of less carbohydrate. Get a glucose tolerance test with your next blood work. Meanwhile, since you're riding a lot less anyway, cut back on your carbs considerably in your daily diet. Half a plate of veggies, 1/4 carbs, 1/4 protein. Maybe you're just hammering your Islets too hard and they need a rest. Been there. No carbo snacks during the day. Fat or protein only. Except after riding, when you need your normal high carb recovery.
Could be more than one thing driving this, which makes it hard to figure out.