In Blender 2.82 it was possible to render AO pass without having it enabled in the Scene. In Blender 2.83 you could only render the AO pass when it was enabled in the Scene. The reason behind this change is that rendering the AO pass influeces the light in EEVEE surface shading. There could be a case that the scene AO was disabled but as the AO Pass was enabled the AO was visible in the Combined and Light passes.
We could add some logic around the AO pass to bind the texture when performing the surface shading.
See https://devtalk.blender.org/t/issue-with-blender-2-83-vs-2-82-ao-is-this-a-bug/13514 for more context