Vanilla bug https://bugs.mojang.com/browse/MC-165504.

I'm not sure if this is a rendering thing or it's somewhere else such as defined in the block's code, so it could be out of Sodium's scope, but there's still a possibility.

The end portal frame appears completely unaffected by ambient occlusion regardless of whether the resource pack in the bug report is active or not.

This may be due to end portal frames emitting light.

165504 is now deemed a duplicate, am considering possibly redoing this ticket to encompass more light emitting blocks