Incorrect Pace with Rolla Band

When I use the Rolla Band as the source for pace, I get quite inaccurate results.
It’s impossible for the band to give perfect results, but the spikes are quite significant.

I consistently run at a pace of 10-11 km/h, yet the Rolla Band displays it differently compared to the Runn sensor, which reads directly from the belt. (Note: the readings can't be exactly the same due to the direct measurement from the Runn sensor).

Here are pictures with both sources for same run.