The MaxReceivedMessageSize is being surpassed for large imports - ~500,000 entities and upwards.
A quick fix is to simply edit the MaxReceivedMessageSize to be its maximum value:
maxReceivedMessageSize = "2147483647"
However, this may only be hiding a more ingrained systematic problem - Why is the IDB Service sending a SOAP message that would surpass the recommended configuration?.
A determination needs to be made about the correct course of action with regards to this behaviour.
Customer support service by UserEcho