Redo Logs Mysql Cluster
Each data node's redo log has a number of 'parts' - currently 4 by default.  Each redo log part is like a mini redo log, with 1 / Num_parts of the capacity defined for 'Redo log'.  This design increases file system and lower layers parallelism when writing the redo log, but requires balance across the parts to be reasonable.

When a table is created, table fragments are created on each data node.  Each fragment is assigned a redo log part which will be used to log all of the activity on the fragment - e.g. inserts, updates, deletes.  

A table with only a single fragment on a particular data node will use only one redo log part, and you will see an imbalance in the use of the redo log parts as you have shown.

Where a table has multiple fragments stored on a data node, they will use different redo log parts, and the use of the different parts is balanced.

Where you have more than one table, the fragments of other tables will use different redo log parts, and the use of different parts will be statistically balanced.

So try creating the single table with more fragments (increase MAX_ROWS, or specify PARTITIONS=X in the CREATE TABLE statement), and see if the redo log part usage is more balanced.