nsh2111 - The tests we take are just snapshots in time. In your shoes, I would consider either investing in a Libre to see the 24/7 trace or testing every hour, in addition to the testing you are currently doing. It could possibly be you are dropping, but having bit of a liver dump, which raises the blood sugar, before you then test pre-food. Only more information would tell you that.
Otherwise has you diet or the quantities you are having change? Have you started a new batch of strips in the last few weeks? Sometimes a batch will read higher or lower than the others.
It's very frustrating for you nonetheless. If you can't pin it down, a chat with the medics could be useful.