Garden Ops wave cannot be completed last enemy not spawning

Is this happening on Time Park?  I've had problems with enemy characters getting stuck around the teleporters in Time Park.  If there's more than one, then they won't have indicators showing where they are.  If there's only 1 left (which is usually the case), a marker will show where it is.  They are usually in the "Hub" room which connects to all of the themed zones (the 1 with a concession stand in the middle and 4 teleporters).  The character is usually in one of the corners of the room nearest to the teleporter.  It seems like their pathfinding sometimes bugs out and they don't understand how to use the teleporters, so they get "as close as they can" to the garden which is the corner of the "Hub" room closest to the garden.

I've had this happen too, but I could eventually see their icons when a teammate walked 'near' them. And when I mean near them I mean over them - they spawned underneath the map. Both times this happened for me it was caused by a specific engineer-built teleporter (on Time Park, in Azia next to the portal that leads to Zgypt) that somehow spawned browncoats underneath the map. I wonder if other engineer/rose built teleporters can do this as well. I made a thread about that earlier but I'm not sure anyone saw it.

Anyhow, I've seen people reporting similar issues with the last enemies not appearing around here before and I suspect that in most or at least some of these cases they've ended up underneath the map, like what happened to me.

So, just wondering, do you remember if there were engineers present who at any point built a teleporter when this happened to you?

The Zen Peaks map was the one that messed up recently for me, it did it twice the same night playing with random groups. One match it was plant side, the other time it was Zombie. I am guessing you are right about one spawning below the map or something, since when it happens there's no way to actually find/get to the last one.

what wave is this happening on? does it happen during a specific challenge?

Those two instances happened during a special challenge, the plant side wanted chickens collected, the zombie side wanted candy (?) collected, not sure what exactly since we failed it as nobody could reach the first object in time, so then we went about the usual killing spree and got stuck with a missing kill.

It happened to me too except I was on Boney Island and I completed the checkpoint race and the zombie would not appear

Literally just happened to me too, same exact map and checkpoint race too