You may need to check the run history and logs of your ADF pipeline for any errors or warnings that could indicate why data is not fully migrating.
Also don't forget that insufficient throughput on either the source or the sink container can cause incomplete data migration. Try increasing the Request Units (RUs) for both containers during the migration process.
One other thing, consider using ADF Data Flows instead of Copy Activity for more complex transformations and handling large datasets. Data Flows provide better control over data partitioning and can help in managing the load more effectively.