Entry Event stopped finding contacts after 365 days

One of our Entry Events in Marketing Cloud Journey Builder stopped admitting contacts. It uses a Data Extension to get the contacts. The issue was discovered on September 17, 2026, but the last contact entered the journey on June 2, 2026. Since then, over 6,000 new records in Salesforce that should have entered the journey have not been admitted. The Entry Event stopped working exactly 365 days after the Data Extension was created (6/3/25), which may indicate an expiration or configuration issue. No errors are reported; contacts are just not entering as expected.  

Other aspects of our Marketing Cloud seem to be fine, including many 1-off sends. 

Any suggestions?