Some players may experience issues with receiving drops in game if they have security software such as an antivirus or firewall blocking the game.
Make sure the game is on any allowed/ignore list for such software. If it already is and you are still experiencing this issue try removing it and re-adding it.
Players should also add exception for the following:
and / or
over port 80
In some rare cases, your ISP may be blocking communication on this port and logging into your account from another location should grant the items. We are looking at a solution for this particular case.
Additionally the steps in these articles may help as well:https://support.killingfloor2.com/en/steampc-knowledgebase/article/item-or-inventory-is-missing-purchased-and-earnedhttps://support.killingfloor2.com/en/steampc-knowledgebase/article/manual-steam-file-refresh