Edit: I guess I need to tag @Ady and @SimonKJones, as I always seem to post bugs reports just before a weekend and by Monday it'll be on page 4.
I'm not sure how much of this is due to the Boris Plugin itself (uses its own lights) or Hitfilm's render engine, but the lighting on the text when it's not very brightly lit has a lot of banding in it. Grey Metal has weird purple bands on it as well as square artifacts, so the banding isn't even very smooth.
See the first few seconds of the video below.
Before anyone says that it's a compression thing, it looks exactly the same inside Hitfilm with Anti-aliasing turned on or off in the Viewer and in both 8 and 16 bit render modes in the Project and with a ridiculously high bitrate on Export. It just really does look like that.