MongoDB updating elements in array of objects from google functions

Question

I have a collection for tracking some tasks performed by google functions

{
    _id: someid,
    tasks: [
        {
            taskId: "1",
            status: "PENDING"
        },
        {
            taskId: "2",
            status: "PENDING"
        }
    ]
}

Whenever a task completes, it updates its status by taskId to COMPLETE and this is working fine functionality wise. The problem I'm facing is the number of tasks in tasks array can be in thousands, and at a point in time, there can be dozens of function instances trying to update the same document and it's causing high CPU usage. Is there a better way of modelling this collection for updates ?