If you use some Megascans surfaces there is a common bug where the Megascans material sometimes gets created with constant value of 0 (completely black) plugged into the AmbientOcclusion material slot.
This won’t have an effect as long as the project has “Allow Static Lighting” project setting remains at the default ON state.
But it will cause black shadows on any meshes using Megascans base material as soon as this setting is turned off, since it allows Lumen to utilize the material’s AO value.
I’ve ran into this quite a few times. It could be your case too. Even if you don’t use Megascans, I’d still check the materials on problematic models if they don’t have black/0 value fed into the AO input slot.