Update from 4.14.1 to 4.18.3 messed up emissive lighting.

I decided to finally update from engine version 4.14.1 to 4.18.3, but it caused one of my materials to change appearance. As you can see in the attached image, I did not change the material after upgrading. Can anyone explain why this is happening, or help me revert to the old appearance? I use this material extensively in my game, so any help would be greatly appreciated.