Tiles layout broken in IE11

[SiAdcock]

Describe the bug

In IE11, a multi-column tile layout looks like a collapsed stack with no margin between tiles

Expected behaviour

Do we could just say that a tile layout is a stack in IE11, and respect y-space between tiles? Or do we fix it so it behaves the same as modern browsers?

Screenshots

IE11

Chrome

Additional context

We could potentially not use CSS Grid. The Columns layout achieves something similar using flex. It's not impossible, just complex.