NPE Runn giving different speed readings on iPad andiPhone

I’m using an NPE Runn sensor on Zwift with my iPad, both ConfigurEZ app and Zwift read 11.2km/h for instance.
Recently the battery died on my iPad in the middle of a run so I had to switch to my iPhone where Zwift was then reading approx 10.2km/h (although the ConfigurEZ app on the iPhone was reading 11.2km/h.

So ConfigurEZ on iPad and iPhone are reading the same, Zwift on iPad is consistent with that reading as well but Zwift on the iPhone is reading low.

Anyone experienced this?