gcloud node api for replacing vms in an instance group not working, but equivalent command line action does

Question

I am trying to programmatically replace VMs in my instance group. This gcloud commandline run within the cloud shell successfully replaces the instances:

gcloud compute instance-groups managed rolling-action start-update INSTANCE_GROUP_NAME --version=template=TEMPLATE_NAME --zone=ZONE --type='proactive' --max-surge=1 --max-unavailable=0 --minimal-action='replace' --most-disruptive-allowed-action='replace' --replacement-method='substitute'

However, the equivalent node code logs as a successful patch operation (just like the gcloud command does) but the VMs never are replaced (ie nothing happens to my VMs):

            const { InstanceGroupManagersClient } = require('@google-cloud/compute');
            const instanceGroupManagerResource = {
            versions: [ {
                instanceTemplate: "global/instanceTemplates/TEMPLATE_NAME"
            } ],
            updatePolicy: {
                type: 'PROACTIVE',
                minimalAction: 'REPLACE',
                mostDisruptiveAllowedAction: 'REPLACE',
                maxSurge: {
                    fixed: 1 // Number of additional instances that can be created during the update
                },
                maxUnavailable: {
                    fixed: 0 // Number of instances that can be unavailable during the update
                },
                replacementMethod: 'SUBSTITUTE' // Method for instance replacement
            }
        };

        // Perform the patch operation
        const [operation] = await instanceGroupManagersClient.patch({
            project: project,
            zone: zone,
            instanceGroupManager: instanceGroupManager,
            instanceGroupManagerResource: instanceGroupManagerResource,
        });

I've tried a ton of different variations here, but nothing has worked. Here's the best resource from google I could find: https://cloud.google.com/compute/docs/instance-groups/rolling-out-updates-to-managed-instance-groups#replacement_method

Can someone help?