Here is a link to your parts breakdown GE STS22ICMBRWW
When it thaws, does it do it relatively quickly?
Faster than if you just unplugged the unit.
How often does it happen? Once a day? Once a week?
Defrost usually occurs at least once every 24 hours, but can vary widely depending on how often the doors are opened because of adaptive defrost control.
Does it thaw while the freezer fan is off, unit is in a defrost cycle?
IF YES
Could be that your defrost thermostat is not opening
It should shut off power to the heater once the coils reach 40 to 50 degrees F, clear of ice but still below room temperature.
If it stays on heat could build up in the freezer causing the melt.
Same thing can happen if the freezer fan stays on during defrost, it circulates the warm air into the freezer compartment.
Am not 100% sure about the above as your unit uses adaptive defrost control
which is located on the control board and they can vary in the way they work.
Check behind your kick plate to see if they have included a wiring diagram and tech information. On many systems there are ways to force the unit into a defrost cycle which would allow you to easily check the above.
Could also just be defrosting too often which would require replacement of the board. | 
