Created attachment 119468 [details] issue.ods - Open the attached spreadsheet - Try to display the grid lines It does not work. (Bug 94921 describes another problem with the same document.)
Go to Menu Tools/options, LibreOfficeDev Calc, View Then at top right, there's a "Grid lines" option, just select "Show" Save your doc, close it, reopen it, it should work (it worked for me)
@Julien: Thanks. I didn't notice that there is the global option that you describe and a sheet property (View/Grid Lines).