When I open a xls file the file name does not appear in the upper left corner and I cannot do a save as and specify where the file is to be saved to. When I do a save as a dialog box pops up which I have never seen before and I have used Libreoffice for some time
5.1.5 is a pre-release version, so expect some (serious or annoying) bugs. You may need to check the LibreOffice bug tracker for reports of bugs in that version.
Open Tools - Options, LibreOffice - General. Is Use LibreOffice dialogs checked? That might explain why you see a strange dialog box.
Do you get an error message when you try to “save as”?