Hi there @Daniel_Golly ,
Unfortunately I’m pretty sure this feature is not available in my tasks. Only in projects can you access the arrow to expand the subtask list. (I don’t THINK this is a change, but I’ve only been using Asana since January and I haven’t noticed it previously being available in my tasks.)
In the desktop or browser version My tasks will still at least show the icon that tells how many subtasks there are in the parent task, but still no expansion arrow. (The icon isn’t even available in the mobile apps.)
There are a few more forum threads about the limitations of my tasks among others. You can upvote them and we hope they will be improved soon. (This one below is on-topic.)
Anyway, hope this at least sheds some light on what your experiencing.