C# Orchestration and firestore

I have a basic Azure function that starts with a timmer (1 min for testing), but after hours of trying to make it work, I can't get my data from the firestore.

The trigger:

[FunctionName("OrchestrationTriggerFunction")]
public async static Task OrchestrationTriggerFunction(
        [TimerTrigger("0 */1 * * * *")] TimerInfo myTimer,
        [DurableClient] IDurableOrchestrationClient starter)
{
  await starter.StartNewAsync("Function1", null);
}

Function1:

[FunctionName("Function1")]
public async Task Function1(
  [OrchestrationTrigger] IDurableOrchestrationContext context
  )
{
  List<string> OrgsToProcess = new List<string>() { "ID" };

  foreach (string org in OrgsToProcess)
  {

    var vehicles = await context.CallActivityAsync<List<Vehicle>>("GetFirestoreVehicles", org);    

    var parallelTasks = new List<Task<Result>>();

    foreach (var vehicle in vehicles)
    {
      // processing code

      Task<CsvResult> task = context.CallActivityAsync<Result>("ProcessData", msg);
      parallelTasks.Add(task);
    }
    await Task.WhenAll(parallelTasks);

    await context.CallActivityAsync("Function2", parallelTasks);
    return;
  }
}

GetFirestoreVehicles:

[FunctionName("GetFirestoreVehicles")]
public Task<List<Vehicle>> GetFirestoreVehicles([ActivityTrigger] string org)
{
  return _firestoreDb.GetVehicles(org);
}

In Function1, on var vehicles = await context.CallActivityAsync<List<Vehicle>>("GetFirestoreVehicles", org); I can see that it has the correct number of records, however all the properties are filled with null.

When looking at the GetFirestoreVehicles during the debugging it says Result = "{Not yet computed}" and I'm unable to use await in my firestore method as it throws the following exception:
multithreaded execution was detected. This can happen if the orchestrator function code awaits on a task that was not created by a DurableOrchestrationContext method

How can I make my Durable Function await the data from firestore?

The GetFirestoreVehicles function should await the result to function properly like this:

[FunctionName("GetFirestoreVehicles")]
public async Task<List<Vehicle>> GetFirestoreVehicles([ActivityTrigger] string org)
{
    return await _firestoreDb.GetVehicles(org);
}

Also, this line is very strange:

await context.CallActivityAsync("Function2", parallelTasks);

You are passing a list of Task<T> to another function. Instead, you need to pass the resulting list of T, not the Task collection itself. Something like this will do:

var results = parallelTasks.Select(t => t.Result);  
await context.CallActivityAsync("Function2", results);

That means Function2 should accept IEnumerable<Result> instead of List<Task<Result>>