whenever i press the "install" button for a modpack i wait the 5 seconds my browser asks me if it can open twitch. i allow and depending on whether twitch is open or not it does one of two things:
if twitch is already open: opens twitch window and does nothing
if twitch is not open: does nothing.
i have no idea what's going on. i have tried clearing my cookies and restarting my device. i have found no other reports of this issue.
You can search it on twitch
Can confirm. This happens with individual mods as well.