If you’re using the SQLite database and another user imports a large volume of data, labeling might slow down for other users on the server due to the database load.
If you want to upload a large volume of data (thousands of items), consider doing that at a time when people are not labeling or use a different database backend such as PostgreSQL or Redis. You can run Docker Compose from the root directory of Label Studio to use PostgreSQL: docker-compose up -d, or see Sync data from cloud or database storage.
For other questions about performance, see What could cause slow performance with LabelStudio?