I've been playing five games at the same time. In the family which is closest to the trophy, I'm missing 4 rare items. But I'm missing different collectibles in each family. The only one I didn't see at all is the rare moth. I found two dragonflies, two purple bugs, a blue butterfly, but no moth in any of the families.

HPVV, I think it's just luck. There are some items which shows up over and over again for the same family, but is missing for another family with me. I think two of the bugs (dragonfly and grasshopper) and a twig (green clover) is somehow hard to see, but all others are easy to spot. Maybe you can download the collectibles mod; I heard it is helpful to spot them.