I just wasted two hours commenting extensively on a document, saving my work every few minutes, closed the document and opened it again to find the comments had disappeared. I just replicated this, twice, with one comment. Close the document and the comment disappears. I’m saving in *.odt, and I have the latest version – 7.3.2.2 (x64). This is simply outrageous. Is there no way to recover this lost work?
Stupid question probably, but have you checked that comments are visible? See View - Comments.
I made a test document with comments, saved and reopened it, and the comments were still there. So, it may be something on your system only.