I have seen something I call a microspike, that I caught once on both the CGM and the meter, and another time just on a meter: https://forum.fudiabetes.org/t/interesting-microspike-caught-on-glucose-meter/211
I think the phenomenon is totally real. The CGM can’t follow that speed, so you see it greatly attenuated on the CGM.
I was interested in seeing what @TiaG wrote:
because, until she wrote that, I was assuming that this speed of rise and fall could all be hormones, not food (I have never seen food make my son’s BG rise that fast – but I can imagine how a toddler might react much faster).
On the other hand, when my son gets a hormone peak (which is pretty much every day), by the time his CGM is at 120 from wherever it started, say, 10 or 15 minutes (in other words when I get the high alarm), his real BG is often around 200. So I know that hormones can be that fast.