Terrible that I don’t know this as much as I’ve played it lol.
Depends on what map you are playing on. On Paradise (the first meltdown map) they are right behind the supply stations at each end of the bridge in the middle. There will be a curved wall and a mini staircase leading to the giant minions. On the second meltdown map (can’t remember its name to save my life) they should be right outside of the big invisible wall thing that leads into the player’s spawn. I don’t have the incursion ones memorized though since I don’t play that mode as much, but I do briefly remember them being somewhere around the sentry protecting the player spawn base.
Also, it’s fine. It took me a while to figure where they are too. Even now I still forget they exist from time to time.