This is a driver bug, and workaround is to set displacement texture filtering to Nearest.
When using World Position Offset and pushing verts of a mesh, cracks appear on the surface using WPO when deployed to an certain iOS devices.
I used the Mobile Previewer to compare results to how they should look on the device, and ES2 actually shows the default grid material and not the material using WPO. It looks as expected when run under the High-End mobile quality settings.
Important This issue does not occur on the iPhone 6, but it does occur on the iPhone 6s, iPhone 7, and the iPad Pro.
1. Open attached project.
2. Deploy to iPhone 6s, 6+, or iPad Pro
Outcome The mesh shows the WPO, but it has significant cracking along the meshes triangles.
Expected No cracks to appear in the mesh. This is how it works on the iPhone 6.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-45391 in the post.