Aurora MySQL Cluster - Massive increase in bytes used

I recently noticed our Aurora MySQL cluster's Bytes Used increased massively from 341 GiB, to 4362 GiB over the course of five days.

The backup logs look like this:

As you can see it rises sharply for a few days and then levels off.

There is no operational reason for this to have happened because our database size is only about ~40 GiB. I upgraded the cluster engine from 2.08.2 to 2.10.2 hoping that the dynamic resizing would take care of the issue, but the bytes used is still showing over ~4000 GiB.

I have rebooted the cluster, but that has made no difference.

Through some research there are a few other resources, but none of them have any real resolution as to this exact issue:

• Why Volume Bytes Used become so high on AWS Aurora RDS MySQL cluster?
• How to stop auto expanding of Aurora's storage (volume)
• Why is my "volume bytes used" always increasing on my Amazon Aurora cluster?
• How do I view the total storage used for my Amazon Aurora MySQL DB cluster?

Engine version:
5.7.mysql_aurora.2.10.2