Please wait for a little bit, reboot the game, and the task should appear.
If you still experience the issue, please reach out to our technical support team, describe your issue and provide the screenshot illustrating it.
We do not recommend completing tasks at the first and the last minutes of the festival. The server is under the highest workload at this time and, depending on your Internet speed and other factors, data processing may take some time, which may lead to a situation when your task will be lost.