Bad things about taking longer breaks from playing the game is that you cannot tell when and why something changed to the worse. I used to keep track of Fan of Knives stacks while playing Natalia RoV build (the stacks building up to 30), but now the counter seems to disappear? Anybody had this problem?
The trouble is resolved. The reason for this misbehavior was that the cubed Lord Greenstone's Fan disappeared from the cube weapon slot - apparently during the patch 2.4.1 procedures. I brought it back to the slot, and now the counter works again.