Thanks! I am always happy when someone plays one of my games.
It is very much a zen-mode, zone out and play, sort of game for me so I don't experience the frustration but I can definitely see why it would be frustrating for people.
I suppose I could halve the number of tiles - either just have 2 duplicates for all 48 tiles or keep 4 duplicates but only 24 different tiles. I think the latter would probably be best. One day I will return to this and make a title screen with different difficulties.