By default, the Interval Auto setting for the Reporting Services chart axis can cause the labels of your X axis to show only every 2nd interval.
Setting the Interval property for the Chart axis to 1 will prevent this behaviour. Select the X Axis on your chart, search the properties window for the Interval property and set this to 1 (will be Auto by default). This article illustrates how to set the interval and provides some basic examples of before and after
You may find it useful to additionally set the Label and Label font properties for the axis. Setting the label font to 6 pt, then disabling autofit and setting a rotation of -30degrees, will ensure you have a better chance of squeezing in longer interval names.