Modpack version
1.79a

Issue
Whenever I start the modpack in the minecraft launcher the game doesn't even appear. It crashes before any window opens and without a crash report, This never happened to me before, only after I updated to 1.79a from 1.78
I tried repairing the pack in the twitch app, but the same error occured.
latest.log

EDIT: After completely deleting and reinstalling the pack it worked fine. But it is still weird that after updating the pack it was so weird.

Logs
Latest log is attached to the issue

You appear to be using outdated Java. This is often caused by Twitch defaulting to an older version than you have available. Follow these steps to update.

• Make sure you have the latest 64-bit Java installed
  https://www.java.com/en/download/manual.jsp Windows Offline (64-bit) is the one you need
• Go to the Twitch Minecraft settings
• Add -version:1.8+ to the Additional Arguments

fw_error_www

fw_error_www

Ok, that is weird... I had the newest Java Version and before the update it worked fine. Whatever, reinstalling fixed it, but thanks anyways :)

Sure thing :)

The real cause of this problem is probably due to a later added version of Vanilla Fix.
Older versions of Vanilla Fix appear to have conflicts with Mods modified after 1.78.
I had a similar issue, which was resolved by updating the Vanilla Fix.