cross-references in writer don't work in pdf export

A few days ago something happened to change the way LibreOffice Writer exports to pdf files. Until then, a cross-reference in a Writer file would become a clickable link in the pdf. I designate certain words or phrases as cross-links (Insert/Cross-reference/Set reference) and insert these in a Table of Contents. The pdf file behaved exactly as the .odt file (click the reference, and the program goes to the target).

Now this does not work at all. The cross-references are not active in the pdf file, and in fact a line that was not active in any way in the .odt file has become active in pdf (“go to page 1”).

Today I updated to LO 6.3.5.2, and it did not change this bug. The previous LO version (I don’t know what that was; maybe 6.0 something) was causing some of this headache, but I don’t have systematic observations.

Update: something is embedded in the file that affects this. Old files (created months ago) work as expected (see first paragraph) when I add new cross-references. And I can delete everything in a copy of that old file, and work as before.

But a newly-created file still behaves as in para. 2. (no active links in the pdf). So I have a workaround, but I find this contradictory behavior worrisome.

Thank you for any help. My OS is Mac 10.13.6 (Macbook Pro).cr