From time to time, we see a brief peak that appears to go down on its own. I have always assumed it was a CGM artifact. This time we captured one that we measured as real:
We tested it manually at 140. We later verified that the CGM was properly calibrated, and that the later 120 level was correct. So this peak, however small, is not an artefact.
FYI, there had been no recent changes in activity, food or insulin.