It was a bit strange to see so much difference as you can see on "pavement" pictures between 7 and 8 Corona versions. Can't accept that the difference between pictures is only by other randomization IDs...
All other versions translations was silky smooth.
In that case I would suggest staying with Corona 7 until you finish the project and switching to V8 only when working on new projects. This is generally a good practice.
In many previous releases we've had similar issues. We try to keep consistency, but can never guarantee 100% identical results when upgrading to the newest version. This is simply impossible, especially with so many changes and new features in V8.
Sorry about that, and please note that the root issue here ("black highlights") is the same in V8 and older versions.