HI,
Are you elements either side of the domain periodic (i.e. along the cylinder axis)? This error comes up when a triangular face is not aligned so that
the top singular vertex is at the same location. In this case direction 1 (bottom) edge is aligned to one of the other edges (dir2).
If the two sides are periodic you might need to use the peralign option in NekMesh to get these faces aligned.
Cheers,
Spencer.