I have a Kala KA-STg that sounds muted when you barre the first fret. I attributed it to my lack of talent, but I have a professional musician friend who picked it up and noticed the same thing.
Hi Gyosh
A quick test is to play a bar chord up the neck, say 4th. If you can play the chord comfortably without the muted notes, your saddle is probably too high. Another way is to hold a string on 3rd position. The string will touch 2nd fret. Now look at the spacing between the 1st fretwire and the string. There should be just a tiny space (one thickness of standard xerox paper is just about right). I bet in your case, you will see more, a lot more.
You have a Kamaka so you can compare. Can you do it more easily on the Kamaka than the Kala?
You can fix it as below. On the other hand, you live in San Jose. Take it to Gryphon Stringed Instruments in Palo Alto. They can look at your ukulele and diagnose your problem. If they are not too busy, they can fix it while you wait. Cost you $20 - $30? Take all of your ukuleles and have them looked at as well. While you are there, check out their ukuleles. The trip will be worth your time.
Lowering the action at the nut is not too difficult. Ideally you use a nut file but you can probably got a set of needle files and use one that "seems right". Tudorp says remove the nut and sand the bottom. Here I respectfully disagree. Sanding the bottom is good only if *all* nut slows are equally too high. And you will still have to put it back, and tune up and test and go back. There also is a danger is not sanding it flat and even.
I would file off the nut slot one by one. You need to do it slow. If you cut too much, you will get a buzz and that's not good. When it happens (it does!), you squirk a small amunt of superglue (with some baking soda), and build up a thickness.
Cheers
Chief