why do i get these lighting errors

i’m very new at unreal wanted to get into using the lighting tools. i decided to play about with the skylight to try and light this interior scene. i noticed some artifacts appearing when i bake the lighting out. the most noticeable is the image at mid settings with the weird artifacts near the top which is the image on the left. they seem to go when i put it on production. however on the wall on the right there seems to be some a lot of noise. i thought this might be a resolution problem so increased it to 512 which is i guess it is quiet large, but it made the noise smaller. how do i get smoother lighting and better results at mid settings.