Look at how the error changes
If every printed outline is displaced the same amount, the problem is usually a position shift. Measure how far the top-left mark landed from its target. A print 2 mm to the right and 1 mm low calls for a −2 mm horizontal and −1 mm vertical correction in LabelNest. Test again on plain paper before feeding labels.
If the first row lines up but later rows drift, an offset cannot fix the sheet. Check vertical pitch: measure between the leading edges of two labels several rows apart, then divide by the number of intervals. A small per-row error accumulates down the page. If both axes drift, inspect print scaling and the chosen paper size.
A reliable check order
First, print the 100 mm calibration line at Actual Size. Second, confirm the PDF page size matches the physical paper. Third, measure label dimensions, top and side offsets, and pitch. Finally, apply a small X/Y correction for any remaining constant shift.
Printer feed can vary from one tray or stock type to another. Keep a successful plain-paper test with your stock package so you can compare it when settings change.