Banded meetup - low speed output for the resistance applied

Attempted a banded meetup around the volcano x25 laps with some friends on Wednesday. For the first three laps our speed output was under 20km/hr with 4 members of the band holding approx 2.0W/kg. Have done this course numerous times and not had this happen before. After approx 40 mins and only completing 3laps (~13min/lap) we quit it and it jacked up to 30km/hr + straight away. Just wondering if this is a common problem for any others?