Try to dip one or two of those acros and see if anything comes off. I have seen the same thing sometimes with them. Color loss is a big one for AEFW. The fact that you don't see bite marks could just mean that your coral is able to overcome but not completely from the stress involved. With that the recession at the base is the other indicator for me. Just too much stress from them and not able to grow as quickly as they eat, so the coral has to suffer some where.
I hope it isn't AEFW, but try the dip to be sure. If wont help and if it is bacterial or something else, the dip should also help with that too.
*had to edit, I misspelled something LOL