Hello!
First of all, how did you set your 3d model? Can you send a wireframe picture? UE4 works better when you have tour wall eedges snapping between each other.
Secondly, How’s your lighting setup, send you world setting, directional light, skylight and lighting quality settings.
This is a very common issue and usually we don’t have many problems solving it, just need to find out what’s causing the issue.
Your lightmap resolution is too low (that’s why the shadows aren’t well defined)
Also, make sure that floor/walls/ceiling don’t extend past each other in the edges