I too have been using Libre for many years. I use mine with a Miaomiao Bluetooth transmitter which talks to my phone.
Like you, I stopped using the reader many years ago as there was just no point.
Over the years I have had only 1 time when I had erroneously high readings. It was the only time that I had a defective sensor, although I have heard other people say that it occasionally happens to them too.
I do often have problems of being stupid high for the first half a day after changing my cannula site.
I have never got to the bottom of why this happens to me, but I suspect it is something to do with my Chubby Belly!
My DSN talked to me about changing sites to my leg or bum. I tried both and wasn't impressed with the results. Perhaps it needs a different cannula for these areas.
I have sometimes wondered if my insulin is a bit dodgy. I have never changed it, but maybe I should next time.
Good Luck