I've been using a resource pack with the snapshots, and up until 17w17b, there's been no issue. But, in 17w18a, the birch trees started showing up as pink and black checkered blocks as pictured, in the same resource pack, stone bricks and cobblestone use varied textures, yet they still work.

The resource pack in question is BdoubleO's pack, downloadable here (linked in the description of his "Building w/ BdoubleO" videos, such as this one). A minimal version of the pack to reproduce this issue is attached, containing only log blockstates/models/textures.