There could be several explanations for this.
If you have uploaded a new emission inventory for the coming year, this result will play a part in determining the new, actual reduction. The absolute reduction does not change, but the relative reduction (%) could change because of this.
If you adapt your climate action plan to the reality and add, remove, or change measures, this will also impact the planned and actual reductions.
If your reference year changes, the relative reduction will also change.