Waaaait..

That is a bit odd. But entries don't get auto-removed after you sync (unless I'm mistaken), only at the instant you are selected as the winner. So you could still enter a bunch of giveaways after winning and those new entries wouldn't get automatically removed after you get the game - you'd need to do that manually. I don't know if you entered anything after the moment you were chosen as the winner, but if so then that's a possible explanation.

Another possibility is that it had nothing to do with the game you won, but that you had a lot of entries to some game that had its GAs mass-deleted. Headsnatchers, maybe?

Maybe there's a couple different versions of the game with different steam ids and steamgifts only removed you from giveaways with the exact steam id that you won.

Edit: There is a base version, silver, gold, and definitive edition.