I’m not sure whether it is a bug. I’ve played this map many times, and it seems random whether the rocket launcher will spawn. It isn’t hidden, but in plain view, yet sometimes it just isn’t there. I usually go through the map in Hard difficulty. I don’t know whether you’re supposed to do something to make it spawn or it is always supposed to be there.
I’ve played the map with Quakespasm, QSS, and Mark V. I’m sure I experienced this in at least two of them.