Everything seems to work as expected on a simple scene. From what I understand you’ve reproduced this on a simple scene as well? Could you share it (or alternatively this particular scene)?
Works fine with Sky and Sun (and Sky only) as well. Are you using the default render settings? Also, could you send a screencap of your exposure control setup (Rendering>Environment (shortcut 8). Or better yet attach the fresh scene here.
Turn off, of raise as needed, Max Ray Intensity in the general render options.
What you’re seeing is the MRI limit come in effect, as the interior is entirely indirectly lit (as your sky is in the background slot, instead of a dome light.).
You’re very welcome.
I left it somewhat implicit, but if you move the sky/hdri into a domelight, you can leave MRI active at defaults, as the dome counts as direct lighting, not indirect.