Strelka sync error on Security Onion 3.1.0

Strelka failed to sync on Security Onion 3.1.0. On the manager node: SOC (webui on the manager node) → Detections → Gear button (on the top right) → Strelka → Full update → Close. See also https://github.com/Security-Onion-Solutions/securityonion/discussions/15938.