One other thing I forgot to mention earlier. Maybe this will apply to your situation? I have a strange issue that happens to me once in a while, usually only when I go outside and its very cold out. In the winter it may happen 3 times a day or once a month, its very random. Out of the blue, my tongue begins to hurt really bad, then I feel like I can not control my tongue and it turns white/greyish. My tongue stops working almost like its paralyzed making my speech barely understandable. For me, its due to poor circulation and cold weather. In my case its probably one of the many after effects from having radiation treatments. I was thinking maybe you have a circulation issue as well due to the scar tissue from your surgery 20 years ago? Try to pay attention to every single thing when you have an "episode". Are you inside or outside, are you cold or is it cold outside, what were you doing just before your tongue got funny, etc. It took me a long time to figure out what was behind my mouth issue. Im telling you to help you get to the bottom of whats going on with your tongue.

Good luck!!!