You'll get better assistance if you supply a packaged workbook or at least an image.
When you partition (use a blue pill) on columns or rows with a line graph, a pane/partition with only one observation in it will be a point instead of a line.
I suspect you're using the Discrete (blue) pill versions of the Discrete Date components.
If your view layout matches this:
You can simply switch from the 2 BlueDiscrete-Discrete date elements of Year and Quarter to 1 BlueDiscrete-Continuous data element of Quarter.
That's a confusing way to say switch your 2 date pills from the above to this (delete your Year pill and right click on your Quarter pill):
This should be the result:
I liked the idea of having a separation for the years, but I guess it won't be possible.
Not as a line graph. But you could always switch to a bar graph if the distinction is important.