I was building a book when this happened

I had a look in the console and it had this error.
It was being spammed in the console VERY quickly (every frame or tick, not sure which)
(Pasted in link because it's a bit big)

It was fixed after reloading the world, though oddly enough reloading the chunks didn't fix it.
Here is what it was meant to look like (not finished)

As you can see on the block one away from the far right has a piece missing, that was the piece that I added when the error started. I removed those bits to try to fix it but reloading the world is the only thing that did. (It is possible that I didn't go far enough away to reload the chunks however. Difficult to test as the error has stopped now.)

Mod List:

• chiselsandbits-8.3.jar
• flatcoloredblocks-mc1.8.9-v1.8.jar
• InventoryTweaks-1.60-beta-33.jar
• jei_1.8.9-2.28.2.166.jar
• journeymap-1.8.8-5.1.3-unlimited.jar
• LLOverlayReloaded-1.0.5-mc1.8.9.jar
• OptiFine_1.8.9_HD_U_H3.jar

I removed mods to see if it would stop happening, it seems to be OptiFine

Please see #7

Yes, its just optifine, for some reason its not compatible with C&B's multithreaded renderer. The issue has nothing to do with shaders, that is just what he named the issue ( I just renamed it ).

Did you see the workaround?

No I didn't, thank you.

I wasn't using shaders at all, I don't even have an shader packs installed, it just did it with optifine installed.