OK, lets go with what WP says about the F-28 code:
The communication between the Central Control Unit (CCU) and
the Motor Control Unit (MCU) cannot be sent correctly.
1. Unplug washer or disconnect power.
2. Check wire harness connections to the MCU, the motor, and
Central Control Unit (CCU).
– Check connections of the CCU board within the housing.
– Make sure all grounding switches are engaged.
3. Check the drive system for any worn or failed components.
4. Plug in washer or reconnect power.
5. Verify CCU operation by running a Diagnostic Test or any
6. Check the MCU by looking for operations of the drive motor.
7. Check the drive motor for powered rotations.
8. Check that the serial harness at the MCU is not mounted
upside down. The wires should be to the left when facing
the MCU connectors.
If you place it directly into a spin-only cycle and it does not run , I would be prone to replace the MCU first. You "found no abnormalities", but that means you don't understand how the CCU and the MCU communicate. As I said, the CCU is looking for motor rotation. It apparently sees none. This means a bad MCU or in rarer cases, the motor. It is easy to OHM the motor, but not easy to check the MCU so you have to go on past experience, and I have a little of that.