Hi Hannes,
To ensure the initial load is aborted properly, firstly you need to abort it in R3AM1. Afterwards, you need to check the CRM outbound queue and inbound queue, in SMQ1 and SMQ2 respectively, to see if there's any relevant queues, if any, delete them manually.
Thirdly you need to check SM50 in both CRM and ECC, to see if there's any relevant work process still running for the initial load. If any, you can select that work process and cancel it.
Regards,
Kamfrk.