I was working on an 8 MB RTF doc. I was saving new versions using Save As (Save As is broken due to a bug). Last three saves, the file size increases to 9 MB, 15 MB and 20 MB with no substantial editing in between, and, what is worse, the LibreOffice hangs on load and never loads the file.
I found an old thread which states that LOW is unstable with large files.
The document took a long time to load, but it finally did load. I copied the content into a new ODT document and the problem seems to be gone. So there indeed was a problem with the file.