Screeding over rubber/foam backing

Pulled up some cord carpet today and it has left a very thin layer of rubber/foam on the floor but is solid,when i say thin under 1 mm.Sharp scraper no good will not touch it so don t think rambo will either.Took all loose off and was going to ardex na over it.Planks going down .When i rub the rubber very hard with fingers little bits of rubber come off.Not sure whether to screed over it or not.

 

Tryed buffer with sanding disc but not touching it,Buffer jumping all over then tripping at box.

 

copper disc