Just read through most of the last stable update thread and it seems your problem has not been reported until now, so i would recommend making a post about it in the relevant thread.
What you could do for now, would be to
-
- use the 390xx driver series, as it is available for your system
or
-
- install the 455xx driver manually by installing the packages required for it and if need be edit/create the necessary config files
Edit:
One last thing we could check though would be if the needed mhwd files are installed. Could you post the output of pamac list -i | grep mhwd?