We have a cement mill of 7.5m in length and 2.8m in diameter which is fed with clinker that was ground in a roll press.
The first chamber is 3.0m in length and has balls 40 to 80mm (30% of filling degree and the following charge: 20% of 80mm, 30% of 70mm, 20% of 60mm, 20% of 50mm and 10% of 40mm).
We made several longitudinal sieving analysis and have observed that the first chamber does not reduce the size in 2.38mm and other sizes (for example in 2.38mm the clinker milled in the roll press has retained 48%, the first sample in the longitudinal sieving has 44% -oversize-, the second 16%, third 20%, 20% the fourth, the fifth 38 %, the latter coincides with the first sample of the second chamber).

The lifter liner is in good condition.
What could be happening?
Is the ball size appropriate?

Thanks in advance!