Hello. Unfortunately there is a bug on the second level that breaks the traps. This was reported by many people and I can reproduce it as well. I tested the first level thoroughly and there doesn't seem to be an issue there. I also can't reproduce the bug you are describing where they can't be placed (in the first level) even when the circle is green. In any case, we will update the game after the game jam with some bug fixes included.
Viewing post in Dead Raiders jam comments
We will do some more testing then. As for traps disappearing - there is a progress bar appearing next to them when you place them and the progress bar goes down indicating that the traps have a timer on them and they expire. This is also indicated with a hourglass icon on their tooltip. Now I added the hourglass icon next to their progress bar to make it more clear. Not sure if this is what you mean though. There is one or 2 traps that isnt visible after placing them because they come from the ceiling and are invisible until a raider enters their area. Assuming that this is what you meant, I added a 3d indicator to the placed traps now that marks their tile as occupied (only traps do this) so you can see more clearly that something got placed there. These update will be included in the post gamejam patch. Thanks for your input!