Update: As of today (April 1) the previous comment view appears to have been reinstated, which perfectly solves the issue I was having with being forced to either start reading comments in the reverse order that I'm used to or having to load up an entire comment thread to get to the newest comments. I'm seeing a LOT of unhappy comments from users lamenting the loss of the Newest First sorting option though so who knows how long until they revert the revert.
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Update 2: It's back as of today, April 9, and they didn't seem to bother actually fixing the Oldest First functionality before rolling it out again.
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Before today's update, the default behavior for comments was to show Oldest First with the most recent comments loaded; older comments would be shown by clicking "View 25 Older Comments" above the comments section. Now, Oldest First loads the oldest comments, and you have to load the entire comment thread to show the most recent comments. I.e., you see this:

How do I get the old behavior where Oldest First loads the most recent comments upon initially loading a ticket?
For the record, I did try out Newest First and it's unusable for me. I've been skipping to the bottom of tickets all day and missing the most recent updates from colleagues and clients because of it.