I haven't had any experience anodizing bead blasted parts, but all of this sounds a lot like anodizing parts tumbled in ceramic media. Simple cleaning isn't sufficient like it is for smooth machined surfaces. I found that the stripped parts (previously tumbled) did better the second time around. I asked myself why, and the only thing I could think of was they were likely way cleaner and down to pure aluminum alloy after stripping.
So, I began trying to clean the parts better in the first place. It took a while, but I discovered they needed to soak in 165º + SP cleaner for several minutes at the minimum.
Things go a lot better when the parts are cleaned in stripper or lye either before or after. Since the lye introduces some level of smut into the equation, they need to be treated in the desmut. Then when they are rinsed of the desmut, they get cleaned a few more minutes in the hot SP cleaner.
Since the parts are actually clean in the most common sense before starting the cleaning, I am going straight to the lye solution first, desmut second, and cleaner last, with thorough rinsing in between.
With the aggressive and extended cleaning process, I have eliminated virtually all uncertainty about if the tumbled parts will turn out. I really think Fibergeek is right about the parts being contaminated by dirty beads and/or air, and better cleaning will be the cure.
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