The issue with graphics not always being visible is a known issue that is unfortunately quite tricky to fix. You can often work around it by playing at a lower resolution or in windowed mode. We hope to fix it in the future, but no ETA on when that might be.
The bug with the Strength Potion duplicating is a more serious bug, and should also be more easy to fix. That for reporting it! We need to look into why it's happening and fix it, hopefully in the next update