I was dealing with this issue for a while. Consensus seems to point toward it being breakdown of the tumbler liner or blasting media. Ive thought it could perhaps relate to desiccant dust, so I removed my desiccant based dryer and installed this in its place. Running this setup ill extract moisture at the first and second drain points but none on the final filters and none out of the filter in the blast itself. It’s pretty dry here in general with seasonal humidity so I think I can get away with no desiccant, other locales may struggle more to implement this setup.
The result has been almost a complete elimination of residue, and I think what’s left is just residual from before. Time will tell if it eliminates entirely or if some is indeed related to the basket and/or media. Thought some of you would find this helpful or interesting.