zip for the repro: https://e.pcloud.link/publink/show?code=XZ5IUrZxTfA7wbGXB0km8sFyaLVLHI9lbdX

Environment

• Adobe InDesign 2026, version 21.0.0.192
• macOS (Darwin 25.5)
• Regression: the same document exports correctly in InDesign 2025 and earlier.

Summary

Exporting a page to Fixed-Layout EPUB fails with an uncatchable Error -29 "Uncaught exception" when
the page contains a large placed raster image together with a vector shape from an
Illustrator-style drawn illustration. The minimal reproducer is just two objects: one large image
plus any single one of those illustration shapes (even a simple 4-point polygon). Removing the image,
or removing the vector shape, makes it export. The error aborts the scripting engine (not catchable with
try/catch); from a panel, the export call never returns.

Steps to reproduce

1. Open min_test.indd (one page: a large image + one vector shape). Or build it: place a large image (~5300×7900 px) on a page and add a vector shape that came from a drawn/imported illustration.
2. Export to Fixed-Layout EPUB (File > Export… → EPUB (Fixed Layout), or doc.exportFile(ExportFormat.FIXED_LAYOUT_EPUB, file, false)).

Expected result

The EPUB is produced, as in InDesign 2025 and earlier.

Actual result

Export fails with Error Number: -29, "Uncaught exception."

What was ruled out (controlled, single-variable tests)

• The image: any large image works (56 MP alone exports fine); the specific file/metadata is irrelevant (pixel data byte-identical, metadata kept or stripped — still fine alone).
• Cumulative load: 8 images totalling 133 MP, or a big image + up to 400 generated shapes, export fine.
• Transparency, strokes, compound paths, bezier curves, rich-CMYK fills: a big image + generated shapes carrying any/all of these export fine (9 separate fabrication attempts).
• Document context / page count / fonts: the page reproduces it alone as a one-page document with the document fonts substituted; other pages and text are not involved.
• Shape complexity / count: a single simple real shape reproduces it just as a complex one does.

=> The trigger is the large image + a single real vector shape whose internal path representation
(from an Illustrator-style illustration) cannot be reproduced by scripted/generated geometry. It is
not size, color, transparency, complexity, count, fonts, or document context.

Reproducer

min_test.indd (attached) — a one-page document with a large image + one real vector shape — reproduces
on export. Package it (File > Package) so the linked image travels.

Workaround

Downsample the placed image (changes the image enough to clear the export), or remove/relocate the
vector illustration from the page.

<!-- History: earlier drafts blamed image pixel size, a specific vector property, transparency, and a
cumulative whole-page/whole-document cost. All disproven by controlled tests (several were artifacts
of the original file drifting under the threshold during a long edit session - a fresh copy always
reproduces). The minimal, reliable trigger is: a large image + one real illustration vector shape. -->