As you are aware, only iPad WiFi & Cellular models have GPS capability. Next you need to consider that GPS is, essentially, a line-of-sight technology - ideally requiring a clear view of the sky for reliable operation.
If you are using your iPad indoors, your GPS may operate with reduced precision - without a clear view of the sky - by receiving heavily attenuated signals or reflected signals that propagate through doorways and other openings. The building construction will heavily influence indoor reception. If indoors, GPS positioning may therefore be unreliable.
Should you be experiencing difficulties outdoors, look for other sources of signal screening - such as the case in which your iPad is installed (if any). Beware of tree canopies - as trees in full-leaf can significantly degrade reception of the GPS satellite signals. If you still find GPS positioning to be unreliable when you have an uncluttered and clear view of the sky, then you might have a fault.