My analysis: The form was too long. The input field asking users for the Member ID wasn't forgiving enough. The instructions didn't display for everyone due to inadequate QA testing of our supported browsers. The member ID card example that we relied on for clarification was never found by users.
My recommendation: Pare down the form to the essential information. Allow users to enter the Member ID with or without the alpha prefix. Integrate the Member ID card icon into the instructions. Move step 4 into an onboarding experience that engages the user after registration is completed.