I think it unlikely it's a calibration issue. Routine calibration for PMs simply make a small adjustments for the strain gauge zero load offset. The effect is quite small. In this case, it may be a setting for the PM, or an issue with communication with the Edge. Check the PM settings (using its related app) and then, if using bluetooth, try using ANT+. There have been some issues using bluetooth with some PMs.
What model of power meter is it. If it is a dual sided model then make sure that both sides are in communication with each otherwise that would halve your value.
