As you can see on the different windows below, it is mostly present here on the active (the file explorer), slightly less on the inactive on the left (mail). On the right, the ShadowFX window doesn't have this problem, and for Edge, behind it, it depends sometimes.
For your information, ShadowFX is set on custom shadow with 40px at the bottom, 20px asides and 5px on top. Transparency is set to 100%, Blur Level on 30% and with a factor of 10px...
