"My luthier checked out one of my ukes that has intonation issues about the 7th fret. No, it's not saddle height, because one string is sharp, and the one next to it is flat."
Nickie, The information you gave (quoted above) suggests that the saddle, and presumably the nut, heights are satisfactory, but adjacent strings are, individually, sharp and flat at the seventh fret. This also indicates that the problem is not one of fret placement. So we have a uke that is set up correctly and has the nut, the frets and the saddle in the right positions. I would deduce from his that the most likely factor which could cause the uke to play flat on one string and sharp on another would be the strings themselves.
How are you judging that these strings are sharp/flat? Can you can hear the difference, and does it spoil the sound of the instrument, or are you measuring with a tuner, and finding a small difference? I ask this because I once worked long and hard to set up a soprano uke so that it played (almost) perfectly in tune, as measured with an electronic tuner, only to find that changes of temperature, humidity, the passage of time, and possibly other factors, meant that the uke responded differently - when measured with the electronic device. A change of strings made it respond quite differently, even though the strings were of exactly the same type.
Throughout all this, the uke sounded fine when played, whatever small discrepancies the tuner revealed. As a result, I now never bother to use a tuner to check the accuracy of every note on each string. If a well set up uke sounds good, that's good enough for me. If it doesn't, I suspect the strings.
I hope this helps.
John Colter.