I'd urge everyone to look at post #8, which perfectly explains what's happening.
Also, please do not let this thread evolve into the typical "how many gifts did you get so far" strawpoll - we have the RNG thread for that (and this thread here will be locked if most posts were to be about that). I'll leave it open for now simply because C4mma's post is helpful and informative and some more people should read it ;-)
I've seen one gift drop. Ever. Drop rate is horrendous. I just assume I'll never see it and if I do it's a nice bonus, but I don't expect to see them in seasons. I don't play a ton hut I put in more than what I'd consider enough to have a shot at getting a couple. Each season I get to around p400.
Until I started farming T8 I did not see any. Yesterday in TX and GR55+ I found 2 in a 5 hour session. I would conclude, like every other drop in the game, you have a higher probability of finding what you are looking for in the highest possible setting you can farm reasonably quickly.
I realize that is an extremely small sample size, yet it is indicative of how the drop rates are calculated in regards to difficulty level.