Problem when saving as docx

I have a problem with my Libreoffice writer 5.4.2.1.0. Many times, when I try to save a file as docx, the writer shuts down because of “an expected error”.

When I open it again the recovery system starts but if I try to save the file again as docx the same problem occurs.

What is going on?
Thanks

Have you saved the file as a normal .odt file first? What system are you using? 32 or 64 bit? What language? ~Is there something special about the file, large number of pages or images, is there function unique to .odt not found on .docx? Is there any reason you cannot use a normal .odt file? The more detail you give, the more someone may be able to help.

Have you saved the file as a normal .odt file first? I don’t remember but I think I did both things.
What system are you using? 32 or 64 bit? 64
What language? Portuguese
Is there something special about the file, large number of pages or images, is there function unique to .odt not found on .docx? No. And it happened with more than one file.

Is there any reason you cannot use a normal .odt file? I use this file on my tablet to give language lessons (as a “black board”). TexMaker is the only app I know that saves changes on .odt but it is not very practical for giving lessons (usually I use Googledocs)…
Thanks

Can you use PDFs on your tablet? Exporting your file as a PDF has far fewer problems than saving to .docx. I would suggest either embedding the .odt file into the PDF when exporting or saving the .odt for future editing.

Also, have you tried saving to .doc instead of .docx? Sometimes, that works out better.

Portuguese version of the question: Erro ao salvar docx

Does the problem still show up in the newest LO version (V 6.4.7 as of 26.10.2020) ?