Has anyone had problems like this? just previously the modifier works fine but just take look at this
2$\begingroup$ Have you applied the rotation and scale? $\endgroup$– Paul GonetMay 29, 2017 at 21:57
1$\begingroup$ It looks like Z-fighting. Make sure you have no duplicate vertices. $\endgroup$– user1853May 29, 2017 at 22:14
Make sure you apply any previous transformation to your curves/mesh (in Object Mode) with Ctrl+A, in my case, X axis was scaled to zero so naturally it became flat.
I did not realized this all the while thinking the only transform I did was in edit mode.
Hope that someone find this helpful as well :)