Use the Viewmodes to narrow down where it’s coming from.
Detail Lighting - All lighting, including diffuse and specular, plus reflection captures, material features(for roughness, metallic, normal), etc. If it appears here, chances are it might be more obvious what is causing it in this view
Lighting Only - Diffuse lighting only. If it’s red in this view, then you can narrow it down to your lighting
Reflections - Disable SSR in the viewport otherwise this mode is hard to look at. But this will show only the pre-computed reflection probes. If it’s visible in here, you can narrow it down to something in the scene contributing during the light bake.
You can also go through the Show tab and start disabling lighting components to see if it’s baked GI, diffuse lighting, specular lighting, etc.