Bedrock Knowledge Base Sync stuck

I have created a Knowledge Base containing 5 pdf files. I clicked the button to sync. Over 10 hours later, the status is still "Syncing". I have tried to delete the knowledge base, but get the error message "ValidationException There is an ingestion job running for the knowledge base with name *****." The string ***** is a substitution I made in the message, but it's the name of my knowledge base.

I believe that the process is stuck. How can I either unstick the process, or delete the knowledge base?