Digital BW, The Print

Hey Mark,
I frame most of my large prints the same way - across the top, with archival linen tape at the corners and in the middle. They're not
quite as large as yours, but this is something I've never experienced. Mine were printed with Piezo Black, also on Photo Rag paper.

Have you spoken with Jon Cone about this? If it's an ink/paper problem, one would think he's experienced or at least spoken with
others who have had a similar problem. 

Not knowing exactly the PH or composition of the glue (does the framer mix it from scratch?), although that may or may not be part of the problem, I was thinking, when you mentioned some diagonal streaks, that perhaps it is the glue, and again [maybe] the back of the tape was
fastened down using some diagonal finger strokes -- perhaps a finger nail, which could push the glue deeper into the paper than the parts 
that were more gently pushed down.

Hope this helps some, rather than making it even more perplexing.

Clay Price