There is no ambient occlusion (AO) effect in the corner.

[gladiator-hy]

This is the image rendered by PBRT. There is no ambient occlusion (AO) effect in the corner, and it even looks a bit bright.
What should I do?

[mmp]

The most likely explanation is that that is an accurate rendering of the scene. If you think there is a bug in pbrt's path tracer, try to find a very simple example scene that shows that there is a bug.

[gladiator-hy]

This time, I only used a simple model.

Here is my pbrt file. "skybox.exr" is too large, and the upload failed.
AO.zip

[gladiator-hy]

After some time of thinking, I think it's because there is light leakage at the corner of the wall. Is this a problem that a path tracer cannot avoid?

[mmp]

That's a reasonable theory. You might try extending the edges of the wall further out to see if that makes a difference. In general, light leaks are not usually a problem with path tracers. See this to learn more: https://www.pbr-book.org/4ed/Shapes/Managing_Rounding_Error.

[gladiator-hy]

Thank you for your reply. I'll study it carefully.