I just ran into a replicable bug where LibreOffice Writer saves data to a random file instead of the filename I provide. How to replicate: ***WARNING*** Read what I write carefully before testing, because this bug overwrites random(!) files. ***WARNING*** 1. Make sure ~ (your home directory; /home/<user>/) is empty, because this bug overwrites random(!) files. While in ~ run: 2. ~$ touch 2020-06-03_test.txt test.txt 3. ~$ libreoffice test.txt 4. File -> Save As... -> 2020-06-03_test.odt 5. Check what happened. LibreOffice will have overwritten a random file in ~. If your ~ is empty except for 2020-06-03_test.txt and test.txt, then test.txt will now be an OpenDocument Text (ODT) file. You can verify this by quitting LibreOffice, and then typing: ~$ file test.txt If other (text?) files are in ~, then LibreOffice will pick any random file to overwrite. Example, you may have todo.txt in ~, then when you save test.txt as 2020-06-03_test.odt it will just randomly decide to dump the OpenDocument Text data in todo.txt.
You are using an old LibreOffice version that is well past its EOL, please try with a recent version, eg. 6.4.4.
This is why, in practice, free and open source software does not work. If you can't be bothered with testing what I've reported with never versions of your software, I request you simply close this bug report. This is my last comment at bugs.documentfoundation.org.
By the way, got this 6.0.7 from Linux Mint itself. I think that's straight from the Ubuntu repository. https://packages.ubuntu.com/bionic/libreoffice-writer But no, this version is too old, so if it destroys files, it's Ubuntu's problem and not yours.
Then please report your bug at Ubuntu, who support the version they provide, the link to bug reports can be found by following the URL you gave.