If you had Factorio 1.0 installed with 0.4.5, then you upgrade to Factorio 1.1, then you will not get an update. I'd suggest making the 1.1 versions 0.5.x
For people who have reported this problem, I've told them to manually download version 0.4.05 from the mod portal here. That works. But it would be nicer if they could update in game.