~~I believe the default sort type is "Active," iirc, and you can change it in your profile settings (top-left hamburger menu, setting, then your profile settings; it's one of the two drop-down menus)~~
Edit: at least I'm pretty sure that applies to both posts and comments, although I realize now that I haven't actually tested that assumption...
Edit 2: This was wrong! I just tested it and it looks like the comments keep their same order regardless of what the drop down is set to! So actually, I have no idea! Sorry! FWIW it looks like the comments are sorted by recency.