The DataShhet of LTC7001 defines the internal charg pupm to 12VDC.
The simulation set this value to 7V if Vccuv is open and 3.5V if this pin is short to GND
Is it a problem of the simulation ?
I have looked at the LTC7001 simulation and internal charge pump voltage (Vbst-ts) is regulated to around 10V regardless of Vccuv is open or shorted to GND. Vccuv does NOT set the internal charge pump output regulation voltage. It sets the VCC undervoltage lockout threshold for VCC pin.
I would suggest updating the LTspice program and rerunning the simulation.
Retrieving data ...