I'm using blender 2.8 and this issue occurred while I was retopologizing something using the poly build tool.
Subdivision surface is create a weird thorn-like curve and I can't figure out why. My unmodified mesh looks fine.
Let me just show you the images because its probably hard to figure out what I'm saying through text alone. I lack the knowledge to accurately describe what I'm seeing here.
UPDATE: So I solved the issue, but I still don't know what caused it.
I selected the whole mesh, and
deleted loose. That gave me a face with 6 vertices. Creating an edge by selecting the two middle vertices and pressing
f recreated the issue; However, using the knife tool to cut the new face solved the issue. I somebody knows what this means, please let me know. Thanks.