SBLM2360T - Timeout error while entering receive mode

I'll state up front that I am somewhat new to motor controllers and BLDC motors. But, I've made other controllers and motors work and I'm willing to dig in and learn. I'm hoping someone can review what I've posted and let me know if I've over looked something or made some other type of mistake.

I have a SBLM2360T connected to a single custom manufactured motor (24 VDC in, 2.38 Nm rated torque, 2000 RPM, 3 phase, w/ Hall Sensors). The motor came with a ZHauto controller that spun it up to max speed, which indicates that the motor works.

I've connected the controller per the instructions to the manual (primary battery for the motor, backup battery for the controller, etc.). The controller is detected by Roborun+. The controller firmware version is 2.0 5/24/2019. I've loaded a SelfTest.mbs script into Roborun+, but when I try downloading "To Device", I get an error, "Timeout error while entering receive mode. Download aborted"

Some research revealed that I should update the firmware; I have the SBLM2XXX-Firmware-Update-v201-111419 version to download to the controller. When I try to "Update Controller Firmware...." (either by USB or COM), it seems to set the controller into a receive mode, which disconnects it from Roborun+, but then the DFULoader Utility cannot find the controller (that is, it isn't listed in the available DFU Device selector) and even when I select the update firmware file the utility instructs me to select a target (but none are available to select). When I try updating by COM, the utility finds the controller, resets it, waits for it to restart and then looses the connection, "The port is closed"

So, I built a USB to Serial adapter and connected it to the RxD, TxD, and GND pins of the I/O connector and tried using Minicom to communicate directly with the controller that way. No luck. At least in Roborun, I can issue runtime queries and get results, but cannot seem to get the motor to spin

I've double and triple checked that the pins in the Molex connectors are seated correctly and there was continuity from pin to contact. For example, there is 5.0 VDC between the PWR and GND of the Hall Sensor connector.

I'm not sure what to try next and would appreciate any thoughts or guidance anyone could provide.