If you have been making any trades recently you may have noticed that the items look like they may not have come through instantly.
Valve have introduced a new "Trade Hold" system on Steam. If you do not have your Steam account connected to the Steam Mobile Authenticator then trades can be held by Steam for up to 3 days to help prevent things like item theft or fraud.
Note that this affects all Steam games that utilize the Steam Economy & item trading, including Primal Carnage: Extinction. For more information on trade holds, please read this.