Now that I have been using Auto Mode for the Medtronic MiniMed 670G for the last one-and-a-half years, I can say that spike control is one of the major weaknesses of this closed loop system.
Auto Mode does a decent job of controlling BGs for low to moderate glycemic index foods. But for high glycemic index foods, the pump struggles because of inherent Auto Mode safeguards.
As a safeguard against hypoglycemia, the pump pauses basal and microbolus delivery following meal bolus delivery for close to thirty minutes. This makes it very hard for the pump to catch up with a meal related BG spike.
In the photo snapshot, as soon as I bolus for my breakfast comprising a cup of tea and a piece of toast, there are purple dots dissapear for close to thirty minutes (purple dots signify every time the pump dispenses a microbolus or basal dose).
According to Medtronic, this period of no microbolus or basal delivery is needed to determine the BG trend after meal bolusing.
Even though the pump resumes microbolus and basal delivery, it is too late and the BG spike is inevitable.
Waiting longer than the 5-15 minutes before eating recommended by Medtronic somewhat helps. But it is still hard to recover from 30 minutes of no insulin delivery.
The reason manual mode is so good with spike control as compared to Auto Mode is because manual mode allows for a good balance between bolus and basal. The user can be able to adjust the basal does just right to assist the meal bolus counteract BG spikes.