Many thanks Matt for your prompt response.
Finally I was able to have some time this morning to get back on the sim and do some diagnosis.
Step 1): I set up a simple PLN flight plan to start airborne at GOXUL (southeast of EGLL) and head toward EGLL, confirmed I was still set up for Live Players / Live Traffic / Live Weather and Time. Last time I flew the sim I had already deleted the Working Title “GARMIN G1000 NXI” from my Content Manager, so for this first flight of the diagnosis I would be flying the stock C172 with the stock G1000. I flew this setup. Other aircraft traffic showed up on the Map in my MFD, with a symbol similar to the default Own Aircraft (white jet) symbol.
Step 2): Then in Content Manager I downloaded the Working Title “GARMIN G1000 NXI”, kept the same Live configurations which I have been using for several days now, and flew that setup. Lo and behold, other aircraft traffic showed up on the Map in my MFD, with the white-outline black-filled tetrahedron symbols plus the relative altitude tags (which as far as I remember is how they appear on the G1000 in the real-life C172SP)! And they also show up fine on the mini-Map on the PFD.
So Matt, after all that I wish I could tell you what I did to get this working, but perhaps deleting the G1000 NXI from my Content Manager and re-installing it was what did the trick!! Anyway I’m very happy to have Traffic working now in the NXI. Here is a screenshot of it working on my MFD. Desktop Screenshot 2022.01.12 - 09.15.52.25|690x388
THANK YOU Matt!