Ah, I would but I've since restarted the game more than once so even the previous log that would've contained the failed start will have been overwritten. Sorry.
Which was because I'm experiencing another annoying behavior with this modpack, but I'm not sure why, so I thought maybe restarting would help. I can make a new post about that on the modpack's discussion board, though. (EDIT: After some sleuthing, it turns out that's just "ChunkyChunks" default behavior and not a bug, so I won't be making that report.)