I just tried another new session - started at Act II, check inventory/vendor and it loads normally, went over to other Acts and the inventory/vendor loading lags.
Went to my settings - this time I only switch the first option Texture Quality to High, tried to check the inventory/vendors and it loads normally. Switched it back to Low after that to continue my game as per normal.
So far now it’s a work-around, the problem is affecting our game play experience and hopes a more permanent fix is on the way.