One thing I have only recently discovered is that bgl meters can be skewed high by immunoglobulins in the blood (antibodies to you and me, that is) So reactions to infections, and vaccines will tend to make certain meters read falsely high, It depends on the technology of the meter and the enzyme chemistry used to sense glucose,
I think the older meters could be more prone to this effect, especially those using GOD sensor technology (Glucose Oxidase Device). However, it may just apply where immunoglobins are used in an IV setting, and may not be causing the problems you are seeing here.
I am a T2D on orals so it is not a problem for me since I am not dosing insulin to counteract. My GOD based meter has shown a recent jump in bgl results, but the newer meter is not budging an inch. I have had my second jab last month.
Edit to add: This may be the mechanism at play during sickness periods other than vaccines. Any invasion by a foreign body triggers an immune response. In fact, even food eaten in a meal increases inflammation, which makes sense since our stomach and gut cannot read a menu in advance of the food cascading in.