Hi ​@belen 

PlanetScope images do not always have the exact same footprint, and pixel positions are not guaranteed to be perfectly maintained across images from different dates, even for the same Area of Interest (AOI). 
For applications requiring precise pixel alignment, additional co-registration may be needed.

Documented in a help center article:
“The footprint associated with a PlanetScope image is an approximation, and the bounding box does not reflect the absolute position of the raster. This is due to the process that creates the bounding box of the raster, so there may be slight differences in the spatial extent between images from different dates or acquisitions” Are the Footprints Associated with the Raster Bounding Box an Exact Representation?.

Here on Planet Community:
“There can be slight spatial misalignments between PlanetScope images, sometimes on the order of 3–4 pixels. The positional accuracy specification for PlanetScope is less than 10 m RMSE for 90% of cloud-free images, but this can be worse in cloudy conditions. As a result, pixel positions may shift between images from different dates, even if they are clipped to the same AOI” 
-​@Mariana Curdoglo  (Product Manager of PlanetScope images)