[MCL-5414] Launcher gets stuck on "Preparing..."

The new launcher won't launch any profile of the game for me. Upon pressing "Play," the launcher either crashes or sits on "Preparing" and must be closed to try again.

What I expected to happen was...:
The game should launch when "Play" is pressed

What actually happened was...:
The launcher either crashes or displays a progress bar with "Preparing" which never advances (even after being allowed to sit for 15-20 minutes).

Steps to Reproduce:
1. Start Launcher
2. Press Play
3. BOOM

This happens with both Vanilla and Optifine profiles which both worked up until the last time I played on this computer (a few days ago). I tried creating a new Vanilla 1.11.2 profile as well to test, and it still gets stuck at the "Preparing" progress bar. It seems like when I try to play with Optifine it just crashes outright, when Vanilla it sits and hangs.

From the Launcher Log (Vanilla):

[0204/093039:INFO:LauncherAppBrowser.cpp(24)] Work dir is C:\Users\joe\AppData\Roaming\.minecraft

[0204/093039:INFO:ClientHandler.cpp(182)] Creating launcher window.

[0204/093039:INFO:LauncherAppRenderer.cpp(110)] Javascript bridge extended.

[0204/093041:INFO:ClientHandler.cpp(846)] Preferences / startup: Read preferences

[0204/093041:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/093041:INFO:ClientHandler.cpp(846)] Configurations: Loading profiles

[0204/093041:INFO:ClientHandler.cpp(846)] Configurations: Loading settings

[0204/093041:INFO:ClientHandler.cpp(846)] Session: Read authDB

[0204/093041:INFO:LocalVersionProvider.cpp(81)] Looking for installed versions in C:/Users\joe\AppData\Roaming\.minecraft\versions

[0204/093041:INFO:ClientHandler.cpp(846)] Updating server status

[0204/093041:INFO:GameController.cpp(186)] Reinstancing game callbacks...

[0204/093041:INFO:ClientHandler.cpp(846)] GameStarter: Previous instance(s) found

[0204/093042:INFO:ClientHandler.cpp(846)] Session: Validated token

[0204/093042:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/093042:INFO:ClientHandler.cpp(846)] Session: Wrote authDB

[0204/093042:INFO:ClientHandler.cpp(846)] Changing view to: main.news

[0204/093042:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/093047:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/093048:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/093048:INFO:GameCallbacks.cpp(161)] launcher/launcher (main) info Preparing to launch minecraft client for 1.11.2

[0204/093541:INFO:ClientHandler.cpp(846)] Updating server status

[0204/094041:INFO:ClientHandler.cpp(846)] Updating server status

[0204/094541:INFO:ClientHandler.cpp(846)] Updating server status

[0204/095041:INFO:ClientHandler.cpp(846)] Updating server status

[0204/095541:INFO:ClientHandler.cpp(846)] Updating server status

[0204/100041:INFO:ClientHandler.cpp(846)] Updating server status

If I do this from Optifine (I know you don't support it, but there's no 'errors' in the Vanilla log, so.... maybe the data will help):

[0204/100258:INFO:LauncherAppBrowser.cpp(24)] Work dir is C:\Users\joe\AppData\Roaming\.minecraft

[0204/100258:INFO:ClientHandler.cpp(182)] Creating launcher window.

[0204/100258:INFO:LauncherAppRenderer.cpp(110)] Javascript bridge extended.

[0204/100259:INFO:ClientHandler.cpp(846)] Preferences / startup: Read preferences

[0204/100259:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/100259:INFO:ClientHandler.cpp(846)] Configurations: Loading profiles

[0204/100259:INFO:ClientHandler.cpp(846)] Configurations: Loading settings

[0204/100259:INFO:ClientHandler.cpp(846)] Session: Read authDB

[0204/100259:INFO:LocalVersionProvider.cpp(81)] Looking for installed versions in C:/Users\joe\AppData\Roaming\.minecraft\versions

[0204/100259:INFO:ClientHandler.cpp(846)] Updating server status

[0204/100259:INFO:GameController.cpp(186)] Reinstancing game callbacks...

[0204/100259:INFO:ClientHandler.cpp(846)] GameStarter: Previous instance(s) found

[0204/100300:INFO:ClientHandler.cpp(846)] Session: Validated token

[0204/100300:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/100300:INFO:ClientHandler.cpp(846)] Session: Wrote authDB

[0204/100300:INFO:ClientHandler.cpp(846)] Changing view to: main.news

[0204/100301:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/100305:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/100307:INFO:ClientHandler.cpp(846)] Preferences: Wrote preferences

[0204/100307:INFO:GameCallbacks.cpp(161)] launcher/launcher (main) info Preparing to launch minecraft client for 1.11.2-OptiFine_HD_U_B5

[0204/100308:INFO:GameCallbacks.cpp(161)] launcher/launcher (main) warn Couldn't get hash for optifine/OptiFine/1.11.2_HD_U_B5/OptiFine-1.11.2_HD_U_B5.jar from https://libraries.minecraft.net/optifine/OptiFine/1.11.2_HD_U_B5/OptiFine-1.11.2_HD_U_B5.jar.sha1: HTTP 404: Not Found

[0204/100308:INFO:GameCallbacks.cpp(161)] launcher/launcher (main) warn Have local file C:/Users\joe\AppData\Roaming\.minecraft\libraries\optifine/OptiFine/1.11.2_HD_U_B5/OptiFine-1.11.2_HD_U_B5.jar but don't know what size or hash it should be. Have to assume it's good.

[0204/100319:INFO:ClientHandler.cpp(149)] Shutting down!