Hi @ffusion, thanks for the report and sorry for the disruption — you read it exactly right, new posts were landing at the bottom.
This was a regression introduced in 2.8.0: a new “new-item placement” option defaulted to bottom, which silently changed the long-standing behavior where new posts went to the top. It hit sites updating from before 2.8.0.
I’ve just released 2.8.2, which restores the default to top — new posts return to the top of the list as before. Please update (Plugins → Updates; it should appear within a few minutes if not already showing).
One note: posts created while 2.8.0/2.8.1 was active were already given a “bottom” position, and 2.8.2 only fixes placement going forward — it won’t move them automatically. If you’d like everything back in date order, Settings → SCPOrder → Reset order re-seeds an enabled post type by date; otherwise you can just drag the stragglers. (And if you ever do want new items at the bottom, that’s now an explicit choice under Settings → “New items”.)
Thanks again for flagging it!