Well, I was going to request this post be removed, but it's probably best that instead I eat some humble pie.
A note to everyone: if you're having frustrations, do not hesitate to contact Ultimaker's stellar support channel directly.
Turns out the issue was with a broken wire going to the sensor in the fan housing. I will be getting a new part for this but in the meantime, the fix was to solder the wires in place. Leveling works great now.