The crux of the matter has been difficult to clarify, however from what I can gather it is most likely to compliance of the floor when hitting the track, to the extent that the whole floor acts as a damper
The fia refers to unusual wear patterns on the plank surface and looking at pictures of the RB it seems to wear down the full length of the plank. In the past this would not happen. The wear would be much more biased towards the front of the car.
My interpretation is that effectively the whole plank is now running at times in flat contact with the track, the load is not enough to cause excessive wear because of the compliance now built in and the location of the titanium skid blocks.
The rb seems to exhibit virtually no chattering so the plank damping is doing its job. However the ferrari seems to at times have a lot of chattering so presumably their floor is not working in the same manner.
I expect rb to have been working flat out on an alternative so the impact to be minimal, but it will have cost time and money.
Just to add, the ferrari floor seems to wear evenly as well, so presumably they haven't got as much compliance as rb so still get chattering.