Right now, when you are reading comments, you can click on them to collapse the subthread.

If, however, you are unfortunate enough to accidentally click in the vicinity of the user’s username, it will then go to that user’s page, and when you swipe back, all of the comments will be uncollapsed again.

This is a terrible UX issue because the chances of eventually clicking some username by accident is very high, as you keep scrolling and clicking to collapse subthreads. As soon as you do, everything is expanded and you lose your place and have to collapse them all again.