Congrats on getting the chemo pump removed!
To explain what happened and why the balloon was rendered out. Without using some form of camera plug-in or changing the render property, Defold will only render in objects between the z-axis of -1 and 1. The objects not rendered still exist and can move about, but will not be displayed to the player during runtime. With your project, the character was being moved to the z-axis of 1 by my NavGO, then having the sprite be at 1 also put it above the upper limit and caused it not to be displayed. If you wanted to leave the z-axis stuff alone, you can fix it by using something like this in the main.script:
msg.post("@render:", "use_stretch_projection", { near = -2, far = 2 })
I also recommend changing the background sprite you are using to a z-axis of -1 so that balloons don’t actually spawn under it.
Here’s a reference to the rendering: https://defold.com/manuals/render/
Here’s a reference to the camera component: https://defold.com/manuals/camera/
I recommend not touching either the rendering stuff or trying to program your own camera, it takes a lot of time and unless you have a highly specialized reason to do so, it is not the best use of time. I personally think it is better to use one of the camera plug-ins. I personally recommend this one by britzl : https://github.com/britzl/defold-orthographic