I am guessing it is the analog dial type they sell? This is an on/off style with a dial to guesstimate the temp. The on off nature of these style of thermostats means it will shut off once it gets to temp and not come back on until the probe measures a certain temp. This causes a fluctuation in the temp of the UTH as it heats then shuts off and cools.
It's not a bad thing as long as you keep close to a desired temperature. Now if it varied say 20 degrees that would be an issue but a few degrees swing is nothing.
If however your OCD gets the best of you and you need constant temps, you need to spend the money and get a proportional style thermostat that will send micro pulses of electricity to the heating element to keep it more steady with the range you want.
So it is normal with low cost thermostats and not a problem as long as the range is just a small degree swing difference.
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