I had the exact same thing. I would plummet, need to eat and then go hyper.
For me it was the timing of each macronutrient coming in at different times
I solved the problem by going very low carb ( less than 20 a day) and reducing my insulin by A LOT. In my experience carb counting didn't work at all. In theory it sounded good but I always rode th roller coaster. Now I eat the same macronutrients at each meal during the day and know my exact dose that keeps me steady
Perhaps someone who figured it out can help. I sure couldn't get it right. Maybe if I split doses I could but not interested in that. I think pump users have better luck. Also, besides low carb I need to watch my protein as that will raise me well. I think it's more common in type 1's.