Current Transformer Transformation Ratio Variation
One part of your problem jumps out immediately.


  "and subject them to load 5A-50A". . . . "I am using CS5463 from Cirrus Logic for Energy Measurement. It allows max 250mV peak signal for current and voltage measurement. The IC reads correct Current Values up till 21A"  


From the data sheet :   “With a 10x gain on the voltage and current channel the maximum input signal is 250 mVP”  

The maximum current that your system can measure is (per specification) is 30.3 amps RMS.  

\$ .250/.07 = 3.57 A_p\$  

\$ 3.57 A_p * (60/5) = 42.85 A_p\$  

\$42.85 A_p * .707 = 30.3 Amps RMS\$  

Any data taken where current is greater than 30.3 Amps RMS will be invalid.  

Also, if your load peak current is higher than 42.85 amps, measurement will be invalid.  

You point out that your measurements seem to diverge at around 27 amps, which is near the 30 amps calculated.  Then later you mention 21 amps as the point where measurements seem to diverge. 

Without further information on tolerances on your .07 ohm resistor and current transformers, and schematic on your exact circuit, I cannot help further.