Messed-up lightmapping

Good day,

I’m currently experiencing some issues with a custom mesh i’m trying to import into my game. Since i’m a bloody beginner in 3D-modelling and the stuff that comes with it, lightmapping brings some issues.
I went through the following steps:

Mesh with no UV-Map and therefore no lightmap:

https://gyazo.com/d284778cc028e49a32b0fc7ec85af4b6

both channels are empty:

https://gyazo.com/1780d6f654cd09b17a33309dd5d2dc75

As you can see there’s literally no lightning at all after lightning-build.

I went on auto-creating a simple UV-Map in blender and left the lightmapping-job to unreal:

https://gyazo.com/51da5b0c9e8f0cef5ac79676bf09c246

uv-map channel:

https://gyazo.com/6579fcff161cfc3fac5ef59761b7ff8b

lightmap channel created by unreal:

https://gyazo.com/58b53b96a0bc9293421f3d0b18eaff52

Today i tried creating a lightmap as a second uv-map in blender with the following results:

https://gyazo.com/cf347a6eea22f6912caa04c77844f0bb

uv-map (the same as before):

https://gyazo.com/30652c28850ac6ac413427dbaf00f1e8

blender-created lightmap:

https://gyazo.com/2dc0ad78bbe081ce7261a086425d3a1a

In comparison:

https://gyazo.com/acff2dd0a42deb85514e27b51c509b1f

As you can see there are still plenty of rendering errors although the black parts vary from the blender-lightmap to the unreal-lightmap. Any help would be greatly appreciated! Thanks in advance.