Matrix4.lookAt(): Reverted to previous approach for handling vectors in the same vertical. See 41e86558d11bd3d42fcbf9985ec40db74f92235f

src/math/Matrix4.js

@@ -335,15 +335,8 @@ Object.assign( Matrix4.prototype, {
 
 			if ( x.lengthSq() === 0 ) {
 
-				var t = Math.PI / 2;
-				var c = Math.cos( t ) * z.y;
-				var s = Math.sin( t ) * z.y;
-
-				te[ 0 ] = 1; te[ 4 ] =   0; te[ 8 ] =  0;
-				te[ 1 ] = 0; te[ 5 ] =   c; te[ 9 ] =  s;
-				te[ 2 ] = 0; te[ 6 ] = - s; te[ 10 ] = c;
-
-				return this;
+				z.z += 0.0001;
+				x.crossVectors( up, z );
 
 			}