Hi,
this can happen for two reasons:

• Planet’s Dove (sensors, which acquire PlanetScope) mission is composed of more than 200 satellites (compared to 2 for Sentinel) so the chance of overlapping orbits is significantly higher (it also happens with Sentinel, but just in high latitudes)
• PlanetScope scenes are much smaller than Sentinel-2 ones, so the chance of your AOI being on the border ob two scenes is larger

You can recognise the latter option by comparing sensing time - if it is just a few seconds/minutes away, this is the case, and you can simply let Sentinel to stich these together by setting from/to timestamp to a couple of minutes away.

If the difference is a couple of hours away, we would recommend using the data that were taken between 11 and 12 local time.

thanks for your help