[Nanovelich]

Apparently, this can happen. The disappearing message is immediately following the spotted message, and the black beasts never spawned on the mountain.

[Neus]

Does it happen often?

[Nanovelich]

Would have to get someone else's word on that. I don't often pay attention to the raid.

My assumption is no.

[MegaBlues]

That was the first time I've seen it since the raid was implemented, personally. It might be something new to 1.79b.

[Nanovelich]

MegaBlues might have a point, but I'll point out that we have had successful raid spawns since. If the bug was introduced with the update, it's still a less common case.