Hi,
I was working in the 2018 version of Maya when this first happened and I was set up meters for the grid spacing, then the top, side and front viewports suddenly stopped showing the grid space, I then converted back to centimetres spacing and the grid returned. I've recently updated to the 2020 version and whenever I work in meters the grid disappears, the real issue is that the same problem has now carried over to centimetres. I have the grid display on and I've tried changed the render engine for the viewports (with no avail). My GPU drivers are up to date and Maya also has all the latest updates. I'm completely stumped on how to fix this, any help/ advice would be greatly appreciated.