Please confirm, if you are able to see the 'liked videos' in the liked videos page? Also, clearing your browser's cache & cookies and updating or reinstalling the app often fixes most issues. You may also try using a different browser and keep us posted.
That's odd. 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!