Let me explain. I play at a distance of 8 chunks. I see the mobs from a great distance. I run towards them, and when I'm one or two chunks away, like a loading glitch, the hostile or friendly mobs duplicate. The funny thing is, they always spawn the same mobs, and if they have items, they spawn with the same item.
I don't have a recording. However, to add some information, it only happens when you approach the race directly towards the mobs. Like a loading error in the chunk. Similar to when duplicating arenas or generating a trader farm.
It's possible. But it's curious that the newly created mob has the same item. For example: A zombie spawns with a sword, helmet, or other identifiable item, and the duplicate or new spawn comes out with the same item.
When it happens. Which, as I've already mentioned, isn't a constant, but a variable I've observed after playing the Switch 2 Beta for several days.