Not sure what else to say other than the rear two blades do not engage at startup or at all for that matter

Hi there, thank you for reaching out. Kindly check if the propellers are mounted correctly. If the propeller is mounted in an improper way, the drone will not take off. You may refer to the picture attached in the link shared below and the steps to mount the propellers properly:
{ https://support.dji.com/help/con ... ;paperDocType=paper }.

Thank you for your understanding.