Actually, going low after meals is a common symptom of slowly emerging diabetes. Your insulin production degrades and the first thing to go is the phase 1 response. The phase 1 response is the stored insulin in your islet cells and it is released very quickly in response to meals. Once your insulin production starts to drop you can’t store up much insulin even if you can produce enough insulin response to keep your fasting numbers normal.
I would be that with an A1 of 5.8% and a fasting of 85mg/dl that if you took an Oral Glucose Tolerance Test (OGTT) you would fail. You can do your own at home. Back in 2010 I changed some medication and had a “Honeymoon” for a couple of weeks. I did my own OGTT. You can see the results, I actually did great and while I went a bit high and had some reactive hypoglycemia I didn’t have to severely limit carbs like I had for years. Sadly, the honeymoon was short, if I did the same OGTT today I would have probably have a dramatically different response going to 300-500 mg/dl and staying there for the entire test.