Refrigerator temperature fluctuates wildly
There may be list of reasons based on your refrigerator design. 
1. May be a faulty pump that pumps coolant.
2. May be a faulty leaking capacitor in the circuit.
3. Leaking of refrigerator coolant.
4. Most power circuits have a ceramic round dial shaped capacitor that usually takes power surges when there is a sudden spike. After a few years(1-3) due to multiple surges it is subjected to a wear and tear and finally explodes. It happens many times and is located in coolant pump under a hard shell casing enclosed in hardened glue so that there will not be any visible damage.
5. There may be a leaking door as doors tend to loosen a bit on sides causing an air gap where cooling leaks.

Better call a technician as he can as sess and tell. I it covers warranty exchange for a new product.