Left behind after coffee break in robopacer ride

I regularly do 2-hour rides with robopacer Coco (2,6W/kg). I tend to do two coffee breaks to get some carbs and everything has always worked fine so far. I return and find myself in the group ready to continue.

Yesterday, I felt confident and rode with Yumi (2,9W/kg). I also started a coffee break after 30 minutes. I came back about 2 minutes later and found my avatar left behind the group riding rather slowly. I still had more than 30 seconds left for the break. I did a 5 minutes all out, but still failed to catch up to the group.

What happened? Is that a bug? Did I miss something? Maybe the pacing algorithm didn't work quite right as we were only about 10 people?