Thank you for the suggestion. It’s still blank with sRGB. Only difference i saw is that without the srgb, unreal editor was reporting “Detected Source Alpha: 1”. It does not say anything anymore.
I noticed one thing that the dumped image has all the channel values set to 0. I am now wondering whether the capturing timing has to do anything with it. Any chance that I tried to save before renderTarget got populated? Or may be it got cleared. I am still new with Unreal Engine. Any pointers on the lifecycle practices that I should watch out for?