We were penalized during 3 days at the end of April. We didn't receive any alert or message of any kind, the page just went unpublished. We tried to reach every contact we had and nobody was really useful as nobody really knows how the policy team works. The page went up live after exact 3 days.
The thing is, we did not published anything that might infringe Facebook's policies and no post was deleted from our page. This was the the most strange thing.
After this happened to us a friend of mine had the same issue last week, and we saw several pages going dark for 3 days and even a month.
Don't expect a fast response, try to reach out to every contact that might know somebody working on FB, because sometimes they could get some information from inside the company about the real reason for the penalization. Review your old posts, look for the ones that might be against FB rules and delete them, do the same for the post with high hide and spam report rate. This might be helpful during a review of your content.