yes this is necro, but I am having this EXACT same problem right now
A pack of two mods works perfectly on two of my computers, but on another one the EXACT same pack (all loading from same usb onto curseforge) gets stuck with FML early loading process running and then vanilla minecraft launches at the same time.
For this one computer, with this one specific pack it will do this and end up only playing vanilla.
I cannot figure out what is causing this at ALL. I have tried uninstalling and reinstalling the pack, redownloading the pack, but I can't get it to run.
What could be causing this on only one computer, with only one modpack, all coming from the same source?