Build lighting stuck at 28%

For some reason whenever I try to build lighting for my open world game it keeps stopping at 28%. When i press “cancel” it gives me errors saying this: “InstancedFoliageActor_0 The total lightmap size for this InstancedStaticMeshComponent was too big and it was automatically reduced. Consider reducing the component’s lightmap resolution or number of mesh instances in this component”. Does anyone have any clue on what this means and what I should do to fix it? Cheers.