How far off are we talking? No system can be stronger than it’s weakest link, so the accuracy of your sensor is definitely a limiting factor. That said, the sensors are allowed to be off by 20%, even if most of us expect and get much better of them, so the system is designed with at least that much variation in mind.
Control-IQ doesn’t work without sensor data. It will default back to your programmed profile. Basically just becomes a "dumb"pump that is as safe as you or your medical team programmed it to be.
Reliable sensor data is important for the best results, but there are enough safeties and padding built into the system that it’s not critical to your health. Example, it can only deliver 60% of an automatic correction bolus when you’re too high (something I criticize, so thank you for illustrating one reason for the precaution). It’s enough to get you down out of the clouds, but not enough to bring you back to the target BG, let alone drive you hypo. So there’s a LOT of wiggle room before it’s problematic. Of course, if you’re a lot higher than your sensor says, you run the risk of staying in ketogenic territory for too long if you’re but intervening.
Also, low prevention can’t really work if the pump doesn’t know you’re low, or heading there. No different than with Basal-Iq.
Are you calibrating after the restart warmup? I’m wondering if there’s a way to smooth out that 11th day trouble. My readings come in ridiculously high after a restart, but line up perfectly once it’s calibrated down, hopefully in just 2 partial steps. Some of the restart advice recommends not calibrating at all, though, and it will settle into place on its own within a day. If you want to go that route, you could just turn Control-IQ off for that day.