If you were the one who initiated the group, they will restore immediately. I have found with os 5 that any group that I was invited to would not restore. Best thing to do would have someone invite you back to the group.
from past experience it is a flip of a coin if groups restore and all of them never restore. like joshjamie said, start asking people for reinvites. this is one of the main reason i dont update my OS unless its needed from now on, getting groups back is to much of a hassle