LTM4620A Output Voltage Change Question

hi team

A circuit diagram was designed using LTspice, as shown in the attached picture.
When the voltage on the TK/SS pin changes, so does the output voltage.
Can you explain what the problem is?
The circuit diagram did not observe the reference,
Is there a problem with the design as shown in the picture?
The customer says it is working well and wants proof of the problem.

Vref (V) Vout (V)
1 1.152
1.5 1.522
1.8 1.8
2 1.8
3 1.8

LTM4620A_KI_200226.asc