Here is How to find a lost Facebook Birthday Recap Video.
I had the same issue yesterday/today & had to do a little digging in the Help Community here, but I did finally find the Birthday Recap Video in my Activity Log:
-Went to My Profile
-Clicked "View Activity Log"
-On the left side, clicked on "Videos Watched" (I had to click on "More" to see this option)
-Found it listed there on the date it was created by Facebook.
Now this being said, I had started to watch the video but accidentally navigated away from the page. When I click the link in my Activity Log, the video loads the following:
"Sorry, this page isn't available
The link you followed may be broken, or the page may have been removed."
Hope its not broken & I definitely didn't remove it. Hopefully my answer helps you guys having this same issue, but looks like I need a bit of help myself on replaying the video, haha!!!