[ARCHIVED] [HR] Wild Prairie Grass Lot Challenge not spawning grass

I have this problem as well, of sorts.  I moved a family into Canter Cottage with the Prairie Grass challenge on.  On the first day I completely harvested several piles of neighbourhood grass (I can't remember the exact amount) as obviously when you first move in there is none on your own lot.  I've now played in the lot for 6 sim days and no prairie grass has spawned on my lot at all.  I've turned the challenge off and on again but it made no difference. 

My game IS modded, but based on the OP's extensive testing I'm not convinced my issue is a mod conflict.  I will however go back into the game mod-free to see if that makes a difference.