According to your answer, I think the only way to give a useful answer requires to have an anonymized version of your Excel xml. Please consider to upload a testfile (use the clip icon when editing your original question)
But from my point of view, it sounds a bit strange that you try a way which requires the use of 2 format conversions from Excel to xml and from xml into LibreOffice, while LibreOffice is capable to use Excel’s native format .xlsx. Every conversion is prone to leak information, since no support of a foreign format is hardly ever 100%, and a single conversion (from xls/xlsx into LibreOffice) probably is less prone than a double conversion.