I would second
@Yulkuy 's suggestion that you get slow developing T1 (aka T1.5 / LADA) ruled out, usually by cpeptide and GAD tests (in the UK anyway).
It's not uncommon for LADA folk to find their diminished insulin production responds well to a lower carb diet, but then diminishes more and can no longer cope....
There are a number of possible reasons for unintended weight loss: I would urge you to talk to your GP.
Having said that, you could just not be eating enough calories and a few too many carbs. I guess the potatoes in the evening are an obvious carb hit. As for the daytime highs, you could have dawn phenomena where your liver helpfully dumps out sugar first thing and your body just can't cope....
How do you feel about cheese for low carb high calory snacks?