Check to make sure that the tip is seated properly. Using a heat pad, apply a light force to the tip and push it into the handpiece. Do not use excessive force and be careful not to bend the tip. The force you apply will typically be about 6 to 7 kgf. You can confirm the tip is seated by checking the distance from the end of the tip to the front of the nipple on the handpiece. For the FX-9701, that distance is about 46mm when using a standard T39-D16 tip. For the FX-9703, that distance is about 27mm when using a T50-D06 tip.
If that does not resolve the issue, measure the tips at room temperature using a multimeter. Here are the points that need to be measured. If the value that you measured does fall within the tip's respective range, the tip needs to be replaced.
The T39 tips should measure around 5.7Ω ± 10%.
The T50 tips should measure around 8.0Ω ± 10%.