Hey man, another thing it could be is the connection in between the neck of the guitar and the body of the guitar. If you take the neck off of the guitar and look at where the neck and body join together, you’ll see that at the bottom of the neck, there’s a little PCB board with little pads on it, and on the top of the body of the guitar, there is a little PCB board with pins on it. So, the way this works, is the pins and pads touch when you put the neck into the guitar, and it connects the two so the frets work, but this connection is really sloppy sometimes. I guess the pins just wear out after a while or something, I’m not to sure what actually happens that makes them mess up so bad. But, the way you can tell if that is your problem or not is to apply pressure to the neck of the guitar and pull it backwards. And by, “Pull it backwards” I mean, hold the guitar as if you were going to play it, and then pull the neck of the guitar towards your body. And while you’re doing that, press on the messed up fret(s) and see if it’s gotten any better. If it has, then you’ve found your problem.
So here’s how I fixed it. I took the wires the run from, the PCB board that the frets are connected to, and cut them off with some wire cutters. I cut them right behind the little PCB board that has the little pads on it, like I talked about earlier. I did the same thing on the other side for the PCB with the pins on it. Then, me and my dad soldered each wire together directly. And we soldered them in the same position they were in before we cut them off of their corresponding PCB boards. Then, we just wrapped the connections in electrical tape, and put the guitar back together. And when we tested it, it worked perfectly!
One thing to note it that the only side effect to this is that you cannot take the neck off of the guitar anymore, so make sure to tape off the little lever that you use to take it off. But besides that it’s wonderful! I hope I could help.