A:Answer Sudesh,
To my knowledge, I have heard of no issues with the Nikon D750 hot shoe connection. It may be, as with all cameras, a small batch of cameras may have had manufacturing defects. Nikon has an incredible reputation of taking care of their customers and I would recommend visiting their website and speaking with one of their representatives if this issue pops up. I highly believe they will fix it for you.
Cheers,
David