Hi Yazid,
I'm actually just packing my gear to go away on Friday so I tried my setup for you. I have a D500 so should get similar results to your D850.
My 1.4x is the Kenko Teleplus HD 1.4 DGX. The box states its for Nikon AFS G and AFS E type lenses.
I've never used it with a macro underwater but testing it on land it focussed excellent with the 105mm AF-S but it kept fluttering with my 60mm AF-S and struggled to lock on with this lens. I checked the lens bare and it worked fine.
I don't have a Sigma for Nikon but with my 8-15mm it works great
Hope that helps a little - I was surprised with the 60mm result, but in reality I'd always use a bare 105mm over a 60mm with converter unless its a really specific shot that you needed that exact focal length for
Mike