This.
If you're going to use Afterburner, uninstall Wattman.
If you're going to use Wattman, uninstall Afterburner.

They just don't work well together, I believe because Afterburner uses some admin privileges that overwrite some of Wattman's settings. I have to use Wattman on my 7-GPU rigs because Afterburner keeps crashing at startup (I suspect too little ram might be the cause). But I hate the damn thing.