Sorry for the delay. If you are using Chrome can you right click and "inspect" and then check the Console output to see if there are any warning/error messages. Please send any error messages to email@example.com with your email in the Subject. We will investigate what happened.
Cher Chiu Thank you for sharing the error code. It's probably caused by a temporary server load balancing. We will investigate more. The close of your browser during creating animation shouldn't cause the problem.
Glad to know that the problem is solved now. Please contact us via firstname.lastname@example.org or the in product "Support" form directly if you continue to see the issue.