I didn't know it was called Waffle Rubber, but that is what I have. I have been slowly removing carpet from rooms, and you are right, it is a disaster. I have had a little luck by washing it with Murphy Oil Soap, and while it is still wet, I get a scrapper like you use for paint, or a smaller one, and I just keep working at it. Then I wash with the Murphy Oil Soap some more. Most places, it is gone now, but I still am having to work on the areas where heavy furniture was sitting for years. I got to the point where I did all that I could in those places and moved on until they are now the only places I still see the pattern. I go back to them whenever I have the energy to work on them, and slowly but surely it is fading.

The trick seems to be to have it really wet before you scrape. I worried about using a metal scraper on the floors, but I have not put any scratches on the floor. It is probably all in the angle that you use to avoid scratching. And the floors look great, so there has been no damage.

Good luck.