UMG clipping requires stencil.
Seems like we don't request stencil when creating backbuffer
const int EGLMinStencilBits = 0;
const int EGLMinStencilBits = 8;
Deploy attached project to S8 with Mali GPU
Compare UI rendering to what is rendered in PIE
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-56058 in the post.