DR is growing continuously

An FDB 7.1 server with ongoing disaster recovery is constantly growing in hard disc space.
The “sum of key-values” of the cloned database (secondary) is about ~120 GB.

fdbcli --exec status:

  Replication health     - Healthy
  Moving data            - 0.000 GB
  Sum of key-value sizes - 434.589 GB
  Disk space used        - 510.371 GB

I found this thread - but unfortunately it has no answer