Sentinel 2 Image Registration

In the first few months (6 or so) of Sentinel-2B it was a known issue that there is a shift, along the lines of what you are describing.

Hi,

This blog post describes some of the problems other users have had with multi-temporal registration for Sentinel 2 data: http://www.cesbio.ups-tlse.fr/multitemp/?p=13112

From the same author, there are reports of plans to improve the registration of archival data:
http://www.cesbio.ups-tlse.fr/multitemp/?p=13252