Workflow Alteration Fails When Activities Are Added or Removed (Elsa 3.4)

I’m currently using Elsa 3.4. My workflow includes several long-running steps. During testing, I realized that I should use a sub-workflow instead of relying on ParallelForEach or child workflows. Previously, the structure was set up like this.

Now, I’d like to transition to using bulk workflow dispatch.

when I access xxx/alterations/run in the swagger, it returns a message like:

> "System.NullReferenceException: Object reference not set to an instance of an object.
> at Elsa.Workflows.WorkflowStateExtractor.g__CreateActivityExecutionContextState|10_0(ActivityExecutionContext activityExecutionContext)
> at System.Linq.Enumerable.IteratorSelectIterator`2.ToListNoPresizing()
> at System.Linq.Enumerable.IteratorSelectIterator`2.ToList()
> at Elsa.Workflows.WorkflowStateExtractor.ExtractActiveActivityExecutionContexts(WorkflowState state, WorkflowExecutionContext workflowExecutionContext)
> at Elsa.Workflows.WorkflowStateExtractor.Extract(WorkflowExecutionContext workflowExecutionContext)
> at Elsa.Alterations.Services.DefaultAlterationRunner.RunAsync(String workflowInstanceId, IEnumerable`1 alterations, CancellationToken cancellationToken)
> at Elsa.Alterations.Services.DefaultAlterationRunner.RunAsync(IEnumerable`1 workflowInstanceIds, IEnumerable`1 alterations, CancellationToken cancellationToken)
> at Elsa.Alterations.Endpoints.Alterations.Run.Run.HandleAsync(Request request, CancellationToken cancellationToken)
> at FastEndpoints.Endpoint`2.ExecAsync(CancellationToken ct)
> at FastEndpoints.Endpoint`2.ExecAsync(CancellationToken ct)
> at Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)
> at Elsa.Http.Middleware.HttpWorkflowsMiddleware.InvokeAsync(HttpContext httpContext, IServiceProvider serviceProvider)
> at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
> at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
> at NSwag.AspNetCore.Middlewares.SwaggerUiIndexMiddleware.Invoke(HttpContext context)
> at NSwag.AspNetCore.Middlewares.RedirectToIndexMiddleware.Invoke(HttpContext context)
> at NSwag.AspNetCore.Middlewares.OpenApiDocumentMiddleware.Invoke(HttpContext context)
> at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)"

request body looks like this-

```
{
"Alterations": [
{
"type": "Migrate",
"targetVersion": 189
},
{
"type": "ScheduleActivity",
"activityId": "84eb599efc9df4a7"
}
],
"WorkflowInstanceIds": [
"ca896fc4ba6e4283"
]
}

```

84eb599efc9df4a7 -> which refers to a previous activity, not the one that was deleted (just for context).

My question is:
Is it mandatory to include all existing activities when applying an alteration?
Is it not possible to add or remove activities during the alteration process?