1. Without being able to reproduce the problem, it's impossible to find out why it doesn't exit - and impossible to act on it.

2. But the conversion tool itself - is it LibreOffice? Or is it something that makes use of LibreOffice? That tool itself shouldn't use the default LibreOffice profile - that would avoid interference between it and the interactive LibreOffice instance. But that is a bug of that tool.

To reproduce the issue:

$ touch file.odt
$ odt2sxw file.odt
/bin/odt2sxw:778: DeprecationWarning: distutils Version classes are deprecated. Use packaging.version instead.
  if product.ooName not in ('LibreOffice', 'LOdev') or LooseVersion(product.ooSetupVersion) <= LooseVersion('3.3'):
Traceback (most recent call last):
  File "/bin/odt2sxw", line 1037, in convert
    document.storeToURL(outputurl, tuple(outputprops) )
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
uno.com.sun.star.io.IOException: SfxBaseModel::impl_store <file:///home/vinc17/file.sxw> failed: 0x81a(Error Area:Io Class:Parameter Code:26)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/bin/odt2sxw", line 1282, in <module>
    main()
    ~~~~^^
  File "/bin/odt2sxw", line 1198, in main
    convertor.convert(inputfn)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/bin/odt2sxw", line 1039, in convert
    raise UnoException("Unable to store document to %s (ErrCode %d)\n\nProperties: %s" % (outputurl, e.ErrCode, outputprops), None)
                                                                                                     ^^^^^^^^^
  File "/usr/lib/python3/dist-packages/uno.py", line 507, in _uno_struct__getattr__
    return getattr(self.__dict__["value"], name)
AttributeError: ErrCode

where odt2sxw comes from the unoconv Debian package.

Note: I've chosen odt2sxw as an example, as AFAIK, it always fails with this error and a headless soffice.bin process left behind. But I could also reproduce an error with odt2txt (also from unoconv) on a private OpenDocument Spreadsheet (.ods) file.