I am wondering how long you had been on that insulin dose? Gallbladder infections can happen and you get partial blockages because of that. And they can be stubborn infections. I can only say from experience with one of my dogs in the past.
It turns out she had an infection in the duct? And that she had probably had it for a while, maybe 6 months plus, a blood test showed something was only a little off so they did an ultrasound and spotted it because of that. She had blood work done every 3-6 months because she had stomach issues from a problem of improperly digesting protein. But the type of infection she had is very stubborn too. So she had to be on antibiotics for 3-6 months to clear it up and I gather that’s common with this type of infection.
And when you have infections, your insulin needs go up. Gallbladder and infection gone and you are back to needing a what would be “normal dose”. And that would be decreased too because of weight loss. I think even a 10% weight loss is supposed to make a pretty huge difference on type 2’s usually. So depending how long you had been taking that dose of insulin…
Just an idea! Otherwise other than weight loss, not a clue!