I would recommend first breaking the scene into sub-levels (level streaming) if you haven’t already.
Then, try baking each level separately so you can narrow the number of static meshes for the baking process - it should be faster (it also will help you find problematic static meshes faster).
Regarding the “InstancedFoliageActor_0 The total lightmap size…” - you should enter Lightmap Density mode (Alt + 0 or view mode => Optimization View modes => Lightmap Density) and check that you don’t have anything red/reddish, if you do you should lower its lightmap resolution.
Usually green is the best, but sometimes blue/blueish can be good too - it depends on the details that you need and how complex the mesh is.
Cheers