If you manually restart a checkpoint, you'll lose all the items you used before, even if you had them when you checkpointed. For example, I'm trying to kill some guards with poison darts. I started with 3 darts, used one on a guard, got caught, restarted the checkpoint... with only 2 darts. Fucking dumb.
Oh god the checkpointing! I remember countless times where I had failed full sync objectives on reaching a checkpoint. Select to start from the last checkpoint to be brought to that same point and having to start the mission over to get the full sync. I just don't get how this got through. In most companies, QA do checkpoint sweeps to make sure that stuff doesn't happen. It's passable on games where there's less of a completionist aspect to missions, but AC3 is the very embodiment of completionism.
Don't worry. I was a massive AC fan since the first one (repetitive, yes, but it had a great feel and sense of identity) and was looking forward to 3 being a return back to form and the end of the story. When I finished the singleplayer, I jumped on multi to see if that could hold and not evewn that did. Exchanged it the day after. I constantly felt like i was ticking boxes, dealing with weird UI, bugs EVERYWHERE and the story was complete horseshit. On top of that the multiplayer's main and most played mode was team deathmatch, in which your character is unique in the lobby and it's just a case of finding your target and going in for the kill instead of blending in with AI that looks like you. Why change something that was unique and not broken? and before you go for my throat, I know that mode was in, but it's not the default and thus less players doing it.
Ugh. Count me out of future AC purchases. This game ruined my excitement for the franchise.