Thanks for reaching out. We'd recommend you to uninstall and reinstall the app. Also, switching networks, WiFi to cellular and vice versa might fix the issue. Let us know how it goes.
Appreciate the info. Please send a feedback report directly from YouTube with these steps: https://goo.gl/WdI0BK . While every individual report may not get a direct response, we do review everything and use the details to investigate and fix issues. Thanks!