Footnotes change between saves

Got a number of LibreOffice Writer documents with a substantial number of footnotes (current one I’m editing has 329). I’ve noticed that every time I reopen I need to edit some of them because the letters are different, with new ones added and some deleted. (I’m saving in .doc format btw.) At first I thought it was just me getting confused because I switch between showing and not showing Track Changes and it can lead to some editing mistakes, but I tried editing to correct it, saving the file and immediately checking, and the footnote will have gone back to previous state or be different. How do I stop this? Running 6.2.4.2 on a Macbook Air.

Hi

Please edit your question (do not Add answer) to specify if you are saving in.odt format or in another format ?

Regards