I wonder if perhaps you might have a laser problem. If it were the chemistry, it seems like you would be see the fading issue from start to finish but with the image starting out dark and then fading, it may worth looking at the laser optics.
May I suggest a methodical elimination.
First - to determine if the problem comes from the processor or the imagesetter:
Draw out a piece of film, expose it to daylight and insert it directly into the processor.
(Depending on the results you may also need do an extra test. Darken the area and insert an unexposed piece piece of film to see if it comes out transparent).
If the film comes out dense Black (and totally clear in the 2nd test) - you ruled out the processor as the source of the problem and concentrate at finding what went bad from the imagesetter side.
But, before doing any of the above - check if someone didn't accidentally switch the replenishing tubes, getting Fixer into the Developer section...