It is still most likely that the modified value of "ids.block-size" somehow does not come through. So, are you sure that
all JanusGraph instances are closed before using the new value ("ids.block-size" has GLOBAL_OFFLINE mutability level). Safest is to have a fresh keyspace and one location for the properties to be used for both graph creation and bulk loading.
sorry for asking: does IDS_BLOCK_SIZE equals "ids.block-size"