Black gaps between static meshes in iOS build, what might be causing this?

I finally managed to build my game for IOS (UE 5.3.1), and it runs fine on my 12.9" iPad. There is a weird rendering issue, though: Gaps show up between my static meshes. These aren’t visible on Windows, or my desktop Mac.

I’m a bit at a loss where even to start looking - is this a scalability issue? MobileContentScaleFactor? Float precision on mobile? Anti-aliasing artefact? Something Metal?

If anyone has any ideas what might be causing this, please let me know! Happy to provide more info. Thanks!

Actually, these lines aren’t between meshes, they run right through them -not corresponding to anything in the mesh geometry. They seem to be all horizontal and vertical, unrelated to anything in the scene, as far as I can see.