Motor would have to be 3 phase, a VFD can't run a cap start single phase motor, so there would be no starting cap.
My possibilities, in order of likelihood:
A) If it was a bad winding or connection in the motor and is single phasing, the motor would would act like this for a while (hard to say how long) until the drive sees excessive load current and trips off on overload. When an AC motor gets single phase power, it doesn't know which direction to spin, but it also cannot create full torque either.
B) The other issue that can result in strange operation is if you have the drive programmed to be in SVC (Sensorless Vector Control) mode, which is the factory default setting (parameter A125 = 1), but you have not performed the Autotune procedure from A127. For SVC to function, the drive needs an accurate mathematical model of the motor electrical circuit, Autotuning is how it gets that information. Without that, the VFD is working from an erroneous motor model based on the factory test bench motor and no two motors have the same electrical properites, so the VFD doesn't know how to make yours work correctly in SVC mode. You either have to perform the Autotune, or change to having A127 = 0 to put the VFD in V/Hz mode, in which it doesn't care about the motor model (but you get less accurate performance). We don't know what it is running but if it is a centrifugal pump or fan, you don't need SVC mode, I would go that route.
C) Does it actually run in reverse, or does it BEGIN to run in reverse and you immediately shut it down? Because if you have the "flying start" enabled, sometimes it will move briefly in reverse when starting from a dead stop. It's a known quirk of the technology that allows flying start to work combined with characteristics of some motors that have high residual magnetism when the motor is at standstill. The flying start is looking for back emf to be able to catch a spinning motor, but if the motor is not spinning, yet has high residual magnetism, the drive can sometimes interpret that as it moving. So when you turn it on from a dead stop, it energizes the motor and doesn't know the rotation direction yet. It might reverse it for a second or two before it figures it out, but often times when people see that, they panic and shut it down before it gets a chance to correct itself. The factory default setting is for flying start (A096) is Off, so someone would have had to turn it On. If the replacement drive was not fresh out of the box, it may have had that feature enabled in a previous life.
I always start off by doing a factory reset to defaults before using a used drive, or one I suspect may have been returned to a distributor from the field.
