Please have a look on my fiddle.
When there are more than 11 values on x-axis, the labels are showing in alternative fashion whereas if there are only upto 11 values, all x labels display smoothly. What might be the reason for this? JsFiddle
Labels are shown at every interval of the axis. In some cases, alternate labels are skipped to avoid overlapping of labels. Setting interval to 1 should work fine in your case. Please take a look at this updated JSFiddle.