It's the algorithm used to try to cut down the time lag between blood and interstitial glucose which causes it and I don't mind at all that it does it because it means less red on my graph and if I hadn't reacted to that Libre low, by eating JBs and stopping the drop, I certainly would have been in the red. I just wish it reduced my occasional highs too, but it never seems to work like that above range.
I use Fiasp rather than NR, not that it is much quicker for me as both are sluggish but what I like about Fiasp is that it is gone in 3 hours for me, often less whereas NR would take the full 5 hours to work. What I dislike is that once my levels get into double figures, it seems to turn to water, so I have to stack corrections to make it effective. This works fine for me and I just ensure that I have a couple of JBs at the ready just in case I need to steady the drop if I get to close to the bottom end of my range when the corrections eventually kick in, but it took months for me to gain the confidence (more like reach a point of significant frustration) to just keep jabbing one correction after another until levels stop going upwards and eventually turn downwards. I am not recommending others do this but it is what works for me. I need more Fiasp than I did NR to do the same job but that shorter activity time is a real bonus for me and I only need 45mins prebolus time at breakfast as oppose to 75 mins with NR, which was just impractical. 45mins is manageable. I would not recommend Fiasp to anyone as it can be frustrating and tricky in my experience, but that slight benefit over NR of it just being active for 3 hours for me just tips the balance.