Theoretically speaking, if it's a scene together ( for example a car scene), it ought to be shot together.
Ashutosh's car scene and Nidhi's car scene were shot in the same car- not different cars. For such a scene, a separate frame shot looks odd, doesn't it? The other thing, this is not a one off, but has been happening for a while. If it was a one off, we wouldn't complain, would we?
Also, the non inclusion of AshNI in the same frame became more of a question because the others MB shoots with ( Armaan, Mallika and Hiraman for example), seem to be all done in the same frame. If they were done differently too, then you'd point to it be a production house issue and nothing else.
MB's showing it as a PH issue. I for one am not entirely convinced, but that's just me 😊