How do I correctly use waitUntilInstanceRunning in the JS SDK?

I'm writing a small function to start and stop our staging environment outside of office hours, based on this article.

Currently my code looks like this - edited for brevity.

import { EC2Client, StartInstancesCommand, waitUntilInstanceRunning } from '@aws-sdk/client-ec2';
import { ElasticLoadBalancingV2Client, RegisterTargetsCommand } from "@aws-sdk/client-elastic-load-balancing-v2";

// ...get the InstanceIds of EC2 instances to start...

const startEC2Command = new StartInstancesCommand({ InstanceIds });
const startEC2Response = await ec2Client.send(startEC2Command);

await waitUntilInstanceRunning({}, {
  Filters: [
    {
      Name: 'instance-id',
      Values: [
        STAGING_API_SERVER_EC2_ID,
      ],
    },
  ],
});

const registerTargetsCommand = new RegisterTargetsCommand({
  TargetGroupArn: STAGING_TG_ARN,
  Targets: [
    {
      Id: STAGING_API_SERVER_EC2_ID,
      Port: 4000,
    }
  ]
});

const registerTargetResponse = await elbv2Client.send(registerTargetsCommand);
// ... starts more resources, RDS etc.

Previously, my code was failing because register targets only works if the instance is in the running state, so I added waitUntilInstanceRunning to ensure that the instance is running before it tries to register with the target group. For some reason, the script hangs at the line await waitUntilInstanceRunning, even when the console shows that the instance is in fact running.

The documentation for this command is sparse to say the least, so does anyone know how to use it correctly?

Thanks!