Adding PDF sometimes not getting table of contents_

[sancho-s]

Issue 1:
Zotero has two different ways of attaching a PDF to a Zotero item

1. Via Ctrl+Shift+drag of the PDF into the Zotero item.
2. Via menus and "Attach link to file".

Until yesterday, I found they performed differently. Option 2 created the table of contents from the PDF, Option 1 did not.

Issue 2:
My issue was that add-on [zotero-folder-import] wasn't adding the TOC for imported PDFs.
It was presumably on the side of a Zotfile action, and that is the reason I am posting here.

Today I can't reproduce that anymore (I wouldn't know what changed).
Ctrl+Shift+drag does create the TOC. But items imported with [zotero-folder-import] still do not have the TOC.

On one hand, I don't know now if others can reproduce issue 1.

OTOH, I don't know the causes of issue 2.
Is there any thing else I can contribute to diagnosing this?

This was reported here and here,