I’m a bit late to the party with this one, but there is footage on YouTube from last year where the pope gives a blessing from an upper floor window. After the blessing the pope turns around and starts walking away from the window. After a couple of steps, he suddenly just pops out of existence - disappears into thin air. Some people have taken this as evidence that the pope was never actually physically at the window, but instead had been replaced with a hologram - and that this hologram had been turned off prematurely, before it had moved out of sight. Maybe a decision was taken not to risk the pope’s health during a pandemic. Maybe the pope is a lie? It does look pretty weird.
The video was broadcast on an American news channel. It turns out that there is also footage from other cameras, and in this other footage the pope doesn’t suddenly disappear - he walks into the back of the room, as expected. Case closed.
Except, why did this happen in the first place. Well, the camera was fixed on a tripod and totally stationary, so if the footage used by this one TV station was played out of sequence at all, only things that are moving within the frame would give it away. I’ve seen a fairly convincing video (opens new window) online showing that some video editing tools will loop a video clip if the length of that clip is stretched to beyond the amount of video available. The beginning of the video clip in this instance is at a point in time before the pope appears at the window, so looping around to this empty window shot while the pope is still in frame would make it look like he’d suddenly disappeared.
While this isn’t a definitive answer to the mystery, it at least has the distinction of being plausible - something the alternative theory, of a pope hologram, is sorely lacking.