Diagnosis
Wild swings usually mean the grill is struggling to maintain a consistent fire, which is often a pellet feed issue or a dirty RTD (temperature) probe.
How to Fix It
First, clean the RTD probe (the thin, pointed metal rod sticking into the cooking chamber from the left side). Use a grill stone or fine steel wool to scrub off any baked-on gunk. A coated probe reads inaccurately and makes the controller over-correct. Also, vacuum out the fire pot thoroughly before your next cook.
If That Didn't Work
Check your pellet quality and flow. Damp or overly long pellets can cause feed inconsistency. Also, listen to the auger during a cook; if it sounds like it's struggling or clicking, there might be a jam or a worn auger motor.
Heads Up
If cleaning the probe doesn't help, the probe itself could be failing. They can drift over time and give false readings, which the official Recteq support can help diagnose.