Here is a pic from that reddit post where you can see what you have to wait for around 3-4 minutes in order for the mc launcher to start. -
Basically when trying to click the orange "Play" button it doesn't instantly load the modpack like usual and instead it tries to install a forge version of some sort (library or sth) and it takes around 3-4 minutes to do so. After that all modpacks work fine until you close curse/overwolf. If you start the curse launcher fresh again you will have the same problem of waiting for a library to install.
This hasn't happened before. And also, from what I've seen it doesn't happen to everyone because on my brother's computer everything works fine. (though I should mention that he has fewer modpacks - I'm not sure if it makes any difference.)