Hi Mallik,
Hmmm, apologies for the images. No worries I spent a fair amount of time playing around with it and managed to get to the bottom of the issue.
In File --> Document Properties, there is a new option which says Spreadsheet.
Under that section there's an option (which is ticked by Default apparently) which says "Treat zero as blank cell". So obviously it then treats valid zeroes as blanks and therefore was causing them to not show in my line chart.
When unticked, zeroes display as one would expect in the charts.
Took ages as intuitively this option would be within the properties of the chart objects.
Hope this helps others who upgrade versions...