Environment
macOS Golden Gate; Illustrator 29.x and 30.x, including 30.8.2.

Summary
Saving a document as PDF can omit gradient strokes and other artwork. In a simplified test, some gradient strokes and two images disappeared from the PDF even though they were visible in Illustrator.

Steps to reproduce with the supplied test
1. Open teste.ai in Illustrator and compare the artwork with the reference screenshot. The artwork contains four groups of three gradient strokes and four color chart images, with images positioned in front of and behind strokes.
2. Save the document as an Adobe PDF.
3. Compare the PDF with the reference screenshot and the Illustrator artwork.

Expected result
All four groups of strokes and all four images remain visible in the PDF, matching the Illustrator artwork.

Actual result
In the supplied PDF, the two groups of strokes whose gradient varies across the stroke width are missing, as are two of the four images. The other two stroke groups and two images remain visible. The cause and the effect of stacking order have not been established.

Original document and troubleshooting
The issue was first observed in a more complex document, where text, linked PSD images and vector objects disappeared from the PDF. The artwork displayed correctly in Illustrator and exported correctly as PNG and SVG. The PDF was incomplete in Acrobat and macOS Preview.

The issue persisted across Illustrator versions and after resetting preferences, changing PDF presets, disabling background saving and exporting, moving the document and linked assets to local storage, reducing artwork dimensions, and exporting individual artboards.

Workaround confirmed in the original document
On a copy, expand the affected gradient strokes into filled shapes using Object > Expand Appearance or Object > Expand, as appropriate, then save as PDF again. Previously missing artwork appeared in the resulting PDF. Preserve the original strokes in an editable copy.

Files for investigation
teste.ai: simplified Illustrator test document.
teste.pdf: resulting PDF showing the missing strokes and images.
printscreen-artboard.png: reference appearance with all strokes and images visible.

Please investigate why this document produces an incomplete PDF and whether the gradient strokes are associated with the omission of other artwork.