Quick answer: Unity occlusion culling treating dynamic doors as permanent occluders? Static objects are baked into PVS - mark doors as Dynamic Occludee and use OcclusionPortal for the opening.
Doors open to reveal a room but nothing inside renders because the bake decided the room was permanently occluded.
Use OcclusionPortal
Place a portal volume in the doorway. OcclusionPortal.open = true when the door opens. The PVS sees through the portal at runtime.
Mark doors as occludees, not occluders
Doors are dynamic. Static occluder flag bakes them as walls. Keep Occluder Static off, Occludee Static on so they're culled but don't cull others.
Rebake after marking
The PVS is precomputed. After flag changes, Window > Rendering > Occlusion > Bake or the runtime won't see the changes.
“Occlusion culling is a baked snapshot. Dynamics need explicit portals to participate.”
Author one portal per door at level dressing time. Renaming it 'Portal_Door_Kitchen' on a prefab makes maintenance possible later.