Bookmarks disappeared.

In opening the working session on a Writer / Web file (LibreOffice version 6.4.0) I discovered that the previously defined bookmarks were no longer there. The links to those bookmarks are still there, but the bookmark list is empty. This had never happened in version 6.2.8.

Are they still listed in the Navigator, Bookmarks section?

The Bookmark section of the Navigator, which was full before closing the file, is now completely empty when the file is reopened.

Every time I open, with version 6.4.0, a file created with version 6.2.8 I find the bookmarks list completely reset.

I’m under and everything is OK. This may be some bug in 6.4.0. Has anybody else experience such a behaviour?