From what I read, this past week is finals for many high school and college students, (or this week for others) in the U.S. and Canada, FWIW. That would have an impact on the 18-49 demo. Those viewers might not show up until the plus 30 figures since the viewing delay may be over a week, or via streaming.
(And in my day, spring finals were late May-early June, so the end of April is a bit mind boggling to me.)