Why can't I find/install the upgrade that I just discovered?
There is a bug that pop ups occasionally/randomly when you try to learn a new tech. It will say "You already know this tech" when you really don't. The bug seems to happen most often when using the wall-mounted upgrade consoles. If this happens, you will be unable to get that specific tech from a wall-mounted upgrade console - You'll have to wait until you get the tech from some other source. A drop pod or an NPC, for example.
Source: This Reddit post, my own experience
Since patch 1.07 this bug is now fixed, see patch notes.