I experience this issue for a few weeks now. It started appearing after yum update
(I'm not sure which upgrade it started with).
So from GNOME when I choose to hibernate the system it looks like it does everything (saves the memory to disk and then powers off) but when I turn it on again it just boots like if I hadn't hibernated at all.
I'm not really sure how to analyze the issue so if you could give me some hint I would be glad...