Strelka sync error on Security Onion 3.1.0

Strelka failed to sync on Security Onion 3.1.0.

On the manager node:

sudo rm /opt/so/conf/soc/fingerprints/strelkaengine.state
sudo so-soc-restart

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.