3 Phase motor changing rotation on startup intermittently
There is probably a missing phase. If there are fuses check them. If there is not a blown fuse, you will need to check the voltages on all three phases and trace the wiring to see where you could have a missing phase.
The impeller can probably be turned slowly with very little effort. As the speed increases it requires much more torque from the motor to turn. That is the variable-torque load principal that applies to fans and centrifugal pumps.
If one of the motor phases is not connected, the other two phases draw current and create a pulsating magnetic field, but the magnetic field does not rotate, so the motor does not develop torque. If vibration or the natural flow of the water causes the impeller to move a little, the motor could start in either direction. It only takes a little motion to get the motor started. Once it starts, the motor is able to develop torque in the direction of rotation. The explanation for that is called the double revolving field theory. It is the same principal that allows a single phase motor to be started using a circuit that is disconnected when the motor approaches full speed.