Cross referencing in LO

Is there a problem with the cross referencing system used in LO?

Writing the Impress and Draw guides, I do use cross referencing to figures
and headings. Several times now I get "Error cross reference source not
found" or similar message when I reopen an LO Writer file or move a graphic
frame within a document. The PNG graphic files are in the same folder as the
Writer file and the headings referred to in a document are in the same
document. This happens even after I have run update all and saved the file
before closing.

I do use Dropbox for storage of my working files so that the files are
synchronised between computers. I use an iMac for writing the guides and a
Toshiba laptop running Ubuntu to get screenshots and test the program
against instructions.

I know this problem has been raised before, but there seems to be no
solution yet.

Regards

PeterS