Sometimes the launcher cannot find Minecraft Preview installation

I installed Minecraft Preview App in my PC. I am sure that I can open and play it as usual. I also bought Minecraft for Windows and the launcher also knows it. But when I opened the launcher application, it only found Minecraft for Windows (not Preview) installation. I tried to press the button named "Install" when I selected the version "Latest preview", but it gave me an error message said "Cannot connect ...". I forgot the detail because I AM A CHINESE AND MY ENGLISH IS NOT GOOD!!!!!! Then I used the desktop icon to launch Minecraft Preview. After some times, the launcher may know I am running it and found its installation. Although it is as usual in the end, but I am sure it took >=5 minutes to do it.