Judging from your screenshot, then in the final composition is not GI, that is, when Render region tests, you see the Light Cache thumbnails, but the GI is not mixed into the final render.
To be honest, I find it difficult to determine what exactly did you do to get a preview LC but at the same time it was not to render😁 Perhaps you something namudrili with save / load GI maps. For example, you use a bunch of the Irradiance the Map + the LC and IM in your «From file» mode. At the same time of the IM file (* .vrmap) is missing or does not match the current camera. Then, LC displays brighter previews, but there is GI rendering error, since there is no component of the IM and the final render rendered dark, without GI.