Modpack version
1.80

Issue
White screen-flickering in the Nether

Logs
No log, as this wasn't a crash.

So, this only occurs when looking at blocks. The screen starts flickering like crazy, even faster than in this example (The link is a Gyazo link, as I read in issue #1322 that you won't open .zip files.) I have tried both with and without the Faithful 32x (vanilla and modded) texture pack. This issue is very similar, if not identical, to issue #1322. Please help.

Please supply your latest.log :)
Are you using Optifine and/or VanillaFix?

Yes, I am using both OptiFine and VanillaFix. Although, when I logged in today, the issue was fixed. I have no idea what caused it.
latest.log

Issue #1322 you linked to was caused by Optifine, so that's probably the cause...