Two stupid things to check quickly: Make sure that the lightmaps are using the correct uvs on your objects (ie, that they aren’t using coordinate 2 or 3 or something) and make sure that your uvs are what you think they are. IE, the shapes in the picture you posted look correct–not great, you could definitely improve your uvs a lot, you’re wasting a ton of space, but more or less correct-- but the faces could actually be the wrong faces, like the side being the top and the top being the side.
Your light map does look like it’s stretched, but I’ve never seen that weird, streaking effect before.
Can you post the screenshots with the lightmap visualizer please?
Edit: As a weird aside, this is a cool effect if you could do it intentionally, so it’d be interesting to figure out what’s going on.