I think you may have a defective lot of material. We bought a batch of the BC canvas about a year ago(BC 1446 B6F13A1) that we have slowly worked through, with none of the problems you are running into. I've run it on a Roland FJ 500, and an HP Z3100 without a hitch.
We don't varnish our prints. That's something we leave to the "Artiste's". I gave a sample of BC's varnish to one of our fussier artists to try, and he wasn't happy with it, and went back to using Liquitex varnish, which he claims smells like the same material, but applies more easily. He did say that it took him more varnish to finish his print on the BC canvas, but he was very happy with the material and the finished prints.
Have you contacted BC? If so, what did they say?
regards,
marc sitkin