Hello Eric Zhang,
Welcome to the Microsoft Q&A forum.
The issue you are seeing could be intermittent.
Please check the status of the Integration Runtime associated with the copy activity. If the IR is not running, start it and try running the copy activity again.
When you encounter the error, check the service health from the below URL:
https://azure.status.microsoft/en-us/status
Also, please follow the below troubleshooting docs and see if it helps.
General troubleshooting doc:
https://learn.microsoft.com/en-us/azure/data-factory/data-factory-troubleshoot-guide
Adf/synapse copy activity troubleshooting doc
https://learn.microsoft.com/en-us/azure/data-factory/copy-activity-performance-troubleshooting
If the issue persists, please create a new copy activity and see the behavior to isolate the issue. This will help isolate the issue and determine if it is related to copy activity or with the IR.
I hope this helps. Please let me know if you have any further questions.