Any 3d static object has to have a lightmap setup for it’s exact shape when it’s imported. The issue is that the cube is lightmaped as a cube, but you’ve stretched it out causing the shadow’s inaccuracy. Static objects basically have the shadows painted onto them when you build lighting, like a texture map… which looks bad if the shape has been warped.
If you recreated the wall in 3d software and imported it with a custom lightmap, you wouldn’t see an issue (I haven’t messed with auto lightmap generation… I might look into it later). Although the wall would need a larger lightmap size, specified under the object’s details when double clicked on. The default cube is 64, a wall like that might need 128 or 256 depending on complexity. Really big stuff needs to be broken down into smaller assets to keep the lightmap sizes down or you’ll have memory problems. Max size is 2048, though I try to avoid having any object that large. I have a small, low poly cave broken down into 4 pieces, for instance.
You may run into the problem of static shadows not lining up with dynamic light sources. If you have wavey lines on the ground, you either need a larger lightmap size or need to break the asset down into smaller pieces. I’ve got a temple that i’m going to seperate all the floors out of later to reduce the lightmaps down further. I’ve also had the issue where my character was getting really dark but the environment wasn’t as dark. Turned out that Static Lighting Level Scale under World settings needed to be halved to get the kind of accuracy I needed and fortunately my level sizes are quite small.
Anyway. It’s an unintuitive ordeal but once you get it sorted out, building levels can be pretty cool. For troubleshooting, watch out for using the wrong lightmap channel on imported objects, remap the lightmap after any adjustment, watch out for the lightmap size being too big and breaking things down smaller, tinker with the light settings and world lightmass settings and good luck!