If that's the mill with the 2 inch rollers, I can tell you that buying those upgraded eccentric knobs is very helpful. They NEVER shift.
However, back to your problem. There are two ways that the eccentric adjusters can reach their XX thousandths setting: over the top or up from the bottom. Both of your eccentrics need to be set on the same side (bottom or top). If you've been setting them on one side and they have been popping out, you need to try setting them from the other side of the eccentric. I don't know which side they should be set on so that they don't pop out.