SOS! Speed controller lose control

Situation:GM150,the motor is de-coupled from the load

First run:when the first time to run the motor to 30 r/m in sensorless mode, the speed control,the torque, is ok and stable;

Second run:when change VFD to the mode with encoder,when speed up to 30 r/m from 0, the speed going straight to 50~60 r/m,and the torque is down below 0,and I can't slow it down only if I change the minium power limit from -0.1kw to -2kw,

It's strange that at another VFD having the same parameters,when another motor is running with encoder, the torque is stable,like 200 ro 300 NM when run at 30 r/m,but this one is mostlybelow 0,like -100 Nmwhen running at 30 r/m speed.

No matterwith or without encoder, I have seen the encoder feedback is very true and correct,I observe the encoder feedback on starter and also in the trace,also I check the motor is really running at that speed.

curve without encoder