If you've installed version 1.0.0 or 1.01 you're probably still using a demo of LuSH-101, and you need to be aware that one of its limitations is sound getting out of tune (floating sound pitch) after 30 minutes.
If you have purchased a full version and still sound gets out of tune, you should look at the LuSH-101's About box and check out if your copy was properly activated (your registration name taken from activation key file should be displayed there).