I wanted to list them here so feel free to respond and I will append it. Also feel free to correct me, but this was based on my playing experience on PC, noticed more than few times, so bugs/glitches are ignored.
- Player visible in the mirror
- High grass for hiding
- Blending in crowd (from the Absolution, but it was missing in Hitman 2016)
- NPCs will alarm if they see you carry a sniper rifle although you are dressed as guard/soldier whatever
- Flash grenades during combat
- PIP when someone investigates or when body is found
- If we consider Professional level (being default level) to be something like default level of H2016 which is Normal level, then there are few differences also (this is questionable however):
– suspicious actions in front of the cameras are noticed
– there are few extra guards here and there and the movement of the existing guards is sometimes different.
- Has way more Escalations!
- Missing Casual difficulty level