Has anyone come across this problem?

My Helix lately if I keep the thermostat at 91-92 I can keep a steady temperature, but if i put it at 93-94 the temperature will fluctuate from 91-101.
Is this a fault in my Helix?
Do they warranty them, I have only had it for about 8 months.

I am running a four shelf rack with 4" belly heat

Rich