In some rare cases the reward server may be down or overloaded, which can prevent the reward from being granted. However this happens, over time the reward should be granted to you. If after some hours or days this has not happened you most likely have another issue and the following KB article will likely help you:
https://support.killingfloor2.com/en/steampc-knowledgebase/article/players-not-receiving-item-or-event-drops-pc
The above will also help if seasonal zeds are not properly showing up or appear to have stuck around after a seasonal event has ended.
For those who are specifically just receiving newly earned Dosh Vault crates, see this announcement about the system currently in place and your account being over granted:
https://support.killingfloor2.com/en/announcements/article/dosh-vault-rewards-new-system
