With 12GB you fine. Previously i not see much (if any) PL9 Auto-Brush related issue in the forum (however its an AI side) i think its works at general (works for me fine).
Sometimes the ‘just using aut-brush’ itself not tell the whole situation, may ‘invert shape’ ‘minus brush’ and similar also applied, so may not a bad idea to share your RAW and .dop file, and we can check to rule out things.
May the driver version (quality of the driver on that version) can be a suspect.
Add-on: I see in the meantime you start a new thread about that: Downgrade from 9.3 to 9.2 - may better to continue in there.