It seems a friend and I discovered the problem. I used a spray mould release. When it got into the corners of the bands, it either insulated the corner and the alloy hardened prematurely before it filled the band, or it built up in the corner and clogged it.
I cleaned the mould with acetone, brake degreaser, and bug and tar remover, brass brush and then a soft brush on a dremal tool. Seems to be good now.
I have used mold release on other aluminum moulds without this problem, but I might not use it again.
Thanks for all you guys offering insight.