Is there a way to move tasks between projects

Add relationship would only work for linkages from one task to another.

There isn't a way to switch projects on a task right now. That's feasible, but the controller would also need to manage things like the different task id, the sprint that the task is in etc.

Did you figure out how you added a task without a project, btw? I've seen this before but haven't been able to duplicate it.

Also, what's going on with the "Add Relationship" button in your screenshot? It looks like the task id is breaking the button somehow.

Code is:

$form['relationships']['add_new']['link'] = [
        '#markup' => $this->t('<a href="#" class="button add_relationship" data-ticket-id="%id">Add Relationship</a>', [
          '%id' => $task->getTicketId(),
        ]),
      ];

Maybe I need to add escaping?