Game packs showing up even though I own all parts in them (no giveaway)

That is normal, If you use SG+ you can just add them to your filter and ignore them though. And the gifter is responsible for checking if they own the games in the pack before sending it them, and it is a valid reason to reroll the giveaway.

Read this

He means...you cant Sync DLC,so ppl who got them still can enter GA for whole pack,then no need to activate+resend this to other/trade etc...but there is nothing to do with this,there cant be DLC syncing until Valve do this on their side

It isn't just a thing with DLC. I have games from bundles I bought wks/months ago that still show up. Since I use the Easy SteamGifts extension for Chrome, if I catch it (and the DLC), I just throw it on my blacklist so I do not have to see it. The system isn't perfect and still has kinks in it, but there are ways to deal/ignore it.