Not pre-filling the torque converter can cause issues. While some say it’s not necessary, it’s better to fill it beforehand to avoid running it dry. If the converter isn’t taking fluid, that could definitely explain why the car won’t move—basically, the transmission has nothing to engage with.

Since you’ve already confirmed the torque converter is fully seated (which is a common issue), next step would be to double-check the pump in the transmission. If the converter wasn’t seated properly on first install, it’s possible the pump got damaged. That would explain the lack of fluid circulation.

As for the electrical side—yeah, it’s possible the sensors are tripping the ECU, especially since the manual block might have a different setup for things like crankshaft position or input/output speed sensors. The ECU could be getting confused, thinking something’s off and not letting the transmission engage.

It could also be worth manually priming the torque converter by pulling it off and adding fluid directly, then reinstalling. Also, maybe recheck the fluid level while cycling through gears with the engine running—sometimes it just takes a little bit to work air out of the system.

If all else fails, scanning for codes with a solid diagnostic tool might give you more insight into whether the ECU is causing the issue.