Unwanted changes to large LibreOffice Writer document ?

I have a 78,000+ word, 230+ printed page LibreWriter Office document on Linux Mint which I am constantly editing and adding to. Each time I close it, it is different when I re-open it. Blank spaces are added in random locations and the embedded photos get moved around, sometimes overlapping each other. The number of pages increases by about 5%. No data is lost. Is there a way to prevent this? It causes a lot of grief. Thanks