Current Transformer Analysis giving error
The accuracy class will not be guaranteed for burdens above rated burden or below 25% of the rated burden (IEC spec of 0.2 is tight).
Insufficient  Ampere-turns will affect error at lower current test levels but also affect saturation levels above rated current.  Permeability and temperature of Nickel steel will also affect inductance from Ampere-turns.   This is my understanding no 1st hand experience of this class of CT’s.
Confirm the CT rating and test levels that failed with actual results for margin of error by discussion with OMICRON and OEM.  Then see if another parameter not specified above can isolate the root cause. By all means correlate your test results with factory for “standard” methods by analog correlation of results, rather than pass fail.  Then you may compute /compare accuracy of tester at CT OEM vs your tester and confirm with OMICRON and OEM for a solution.  Replace part , measure/test tester for correlation with calibration  and assess risk of failure and benefit of your new experience in least time+cost.