In some locations the phone might not be able to get good GPS readings. If you are riding in an indoor arena the roof might be too thick and block these signals. Check your signal strength by starting the app and, if you have less than two bars, the position tracking will unfortunately be poor. You can still use equilab, but distance, velocity and stride will become less accurate.
If it is not tracked at all it is probably due to that you did not permit the app to use the GPS. Enable equilab to do so by go to settings > apps > Equilab > permissions. to high precision as well.