I cannot get the hull plate to trim to the centerline on this file. We do it as common practice normally with no issue. What can we do?
Upon checking your model, I assume that you wanted to trim the hull to the centerline buttock plane. What you can try to do is adjust the offset of the hull to 1mm (negative) so that it can intersect with the buttock plane centerline.
Then make sure to set the buttock plane as hull shell (right click | Properties).
From there, you can start trimming. See image below for trimmed hull to centerline.
Designing without trimming
Trimming surfaces with decks