I recently was considering making a Thri-Keen Barbarian since their Chameleon Carapace and unarmored defense seemed like they would work well together and it would make for a fun character; however after making the character I noticed that they don't work together at all. It doesn't make sense that simply choosing a race and class would cause you to lose a feature of one of them. In my opinion, the text of Chamelon Carapace should be re-written to give you a +3 to AC when not wearing armor so that they do work together. It doesn't seem overpowered to me since it would mean that you can add your con mod to your AC as a barbarian. Thoughts?

You select a single AC calculation. Both Unarmored Defense and Thri-Kreen provide calculations for AC, not boosts. A flat +3 to AC would be quite a boost; most racial options for improved AC are not designed to just make a character significantly harder to hit, they're there to give an AC similar to what you might normally reach, just in a different manner.

That's not how any of the natural armors or unarmored defenses work. None of them stack.