@cpa, FWIW, I began encountering today what is a new variant I've not seen before of what you may be calling the "grey graph paper tiles" -- a photo of my CID after I pulled-over and parked is below.
In the past, even in areas with double or triple bars on my AT&T iPhone, my CID Nav has always elected to sometimes not display a few tiles and generally after I leave the area I'm in, or after waiting a sufficient amount of time, the situation resolves. I figure it's transmission issues or the CID processor has what it considers more important things to do. The problem is more prominent when I have a hybrid view on, vs if I use a line-mode only (so I use line-mode nearly all the time the last several months as my personal workaround). I've documented in other threads my reports to Tesla Service and my belief there are memory constraints causing this.
...but this new "grey graph paper" sorta thing looks different to me, or perhaps I'm just in a daze today believing it's different now that you mention it. You'll see it in the picture below towards the bottom of my Nav display what I'm talking about. Oddly, the tiles did not clear themselves as I traveled off the screen and back over a 10-15 minute period of time, and a patch that was off this photo came back as I returned home. I tried rebooting the CID at my midway point after taking this photo, as that has always seemed to clear the cache and jumpstart the Nav/Media Player again, but in my case, the exact same grey tiles remained. ...and also strange now that I look at the photo is some of the street names are upside down or half-and-half. I don't remember that oddity occurring since I took delivery last September, but seem to remember reading it was there in very early firmware releases... Very odd stuff.
Unlike many here seeking out a SC to get the latest firmware, I'm still on tried-and-true 2.20.30, awaiting Tesla to anoint me with the next iteration.