Unexplained disk usage in AWS Aurora Postgres

Hi!

We are experiencing a strange situation with an AWS Aurora postgres
instance.
The database steadily grows in size, which is expected and normal.
After enabling logical replication, the disk usage reported by AWS metrics
increases much faster then the database size (as seen by \l+ in psql). The
current state is that database size is ~290GB, while AWS reports >640GB
disk usage.
We reached out to AWS support of course, which is ultimately responsible.
Unfortunately they were not able to diagnose this until now.

I checked with the queries from wiki
https://wiki.postgresql.org/wiki/Disk_Usage , which essentially give the
same result.
I tried to check on wal segment file size, but we have no permission to
execute select pg_ls_waldir().
The replication slot is active and it also progresses
(pg_replication_slots.confirmed_flush_lsn increases and is close to
pg_current_wal_flush_lsn).

Can you imagine other things that I could check from within postgres with
limited permissions to diagnose this?

Best Regards
Chris