Hello,
as describe in note 1571845 this is normal behaviour to release the heap memory that only gets released when the wp re-starts.
This is not an error.
You could increase "abap/heaplimit" parameter for instance to 100MB just not to so many messages in the system log.
This is kind of safeguarding parameter.
If you don't get memory dumps or memory issues you don't need to change the other parameter settings.
kind regards,
Mercedes