I noticed that comments are differently ordered if there are tons of comments.
What is the ordering? Is it just by upvote?
Comments are always sorted chronologically, however if there's more than a certain amount, then some of the less upvoted comments are hidden and can be revealed using a "Add / show x more comments" link.
Also, remember that comments from this year don't show a date. To see the full time any comment was posted, hover over the date and a tooltip will show the full date and time.