coregistration searches similar patterns in two images to find their best alignment. Coherence has nearly any patterns which occur in both images so this will technically fail.
Speckle filtering your coherence also makes little sense to me because speckle filters are designed to be applied at the backscatter intensity. If you have many images, multi-temporal makes sense at the intensity level. But it makes nearly no difference for less than 6 images if you apply a single or multi-temporal filter.
See here: Single or Multi-temporal speckle filter? - #6 by ABraun