I was unable to see which block in the world is causing this as my pack is also dealing with an entirely irrelevant crash.

A fix in Supplementaries was originally pushed to fix the same issue they were having in their mod as well. the issue is vertex format; if one or more of your blocks has custom code to support dynamic texture building (for say, wood types) if you format it in the wrong way optifine will think some of the values are negative.

[13:16:07] [Render thread/INFO]: [CHAT] §eOpenGL Error§f: 1281 (Invalid value)
[13:16:10] [Render thread/ERROR]: [OptiFine] Suppressed 72417 OpenGL errors: 1281
[13:16:10] [Render thread/ERROR]: OpenGL API ERROR: 1281 (GL_INVALID_VALUE error generated. neither nor can be negative.)
java.lang.Exception: Stack trace
at org.lwjgl.opengl.GLDebugMessageCallbackI.callback(GLDebugMessageCallbackI.java:39) [lwjgl-opengl-3.2.2.jar:build 10]
at org.lwjgl.opengl.GL14C.nglMultiDrawArrays(Native Method) ~[lwjgl-opengl-3.2.2.jar:build 10]
at org.lwjgl.opengl.GL14C.glMultiDrawArrays(GL14C.java:153) [lwjgl-opengl-3.2.2.jar:build 10]
at org.lwjgl.opengl.GL14.glMultiDrawArrays(GL14.java:352) [lwjgl-opengl-3.2.2.jar:build 10]
at com.mojang.blaze3d.platform.GlStateManager.glMultiDrawArrays(GlStateManager.java:2088) [?:?]
at net.optifine.render.VboRegion.finishDraw(VboRegion.java:333) [?:?]
at net.minecraft.client.renderer.WorldRenderer.drawRegion(WorldRenderer.java:2344) [?:?]

the behaviour is random, still unable to find the block at fault. will go hunting for it with superflat creative at some point

doesn't seem to be this mod at fault. closing.