Have you tried to increase the “indirect Lighting” in a global post processing volume, its under the global illumination property tab?
You can also increase the Indirect Lighting intensity in the “Light” properties panel of the light you have in the scene.
Also if you do not have a light mass importance volume covering the area you are trying to bake the lighting at, creating one will help a lot.
From the look of it the UV’s seem to be the most likely problem, but try the things I have listed and let me know.