Ok, so I have this problem, in the first image you have the "final" render, here the glass from the windows doesn´t reflect the light that comes from behind the camera, something that you can see appearing in the "preview" one (which is the one on the right side). If I adjust the gamma in color management, reflections start to appear, but colors start to change too!. Any idea of what could be happening? thanks
There is nothing wrong with your image, so don't try to fix it.
The issue is that the render viewer in blender is broken: the viewer won't show the pixels that are both luminous and fully transparent (alpha zero, RGB not zero) from an image with associated alpha (like the reflection on a window that have no occlusion but are only luminous).
View your render As RGB (without alpha channel) and you will see that your information is there.
Or just composite an image over a background using alpha over.
If you are planing to do the final composite in an app that is not blender, make sure that you save as OpenEXR, to keep the integrity of your image.