Machine holding size

I have a Haas TL1 lathe, I machine Babbitt bearings on this machine using carbide boring bars. My problem is that I can machine 70 bearing the out of the blue I get a bore that is .0015 " oversize, if I run another after the oversize one without making adjustments it is also .0015 oversize.

I change the offset and maybe run another 8 parts and get another one .0015 oversize. I am not sure what is happening, if it was build up edge the bores size would go down at some point. I seems the parts never get smaller only larger. I am trying to figure what is going on, tool wear would make bore smaller, Build up edge would eventually go back to he original size. Wondering if there could be dust in the servo motors that would cause the motors to loose a pulse and change the size ?

Thanks in advance, Mike