With the new task page layout we desperately miss the option to collapse tasks. Specially in projects with a lot of closed tasks (e.g. set of tasks for each sprint) it would help a lot if tasks could be collapsed (as it was before).
The changes we made were, in part, to improve performance. To do so, we updated the list to show 1 page of data at a time and unfortunately expand/collapse functionality does not work well with the new model. We're looking into solutions to support both collapsing and performance, but there's no timeline at the moment. We'll update here as we have more.