I’ve been checking your system status before and as I said previously, this problem usually related to memory usage on the server. Also, there’s no error when this problem occurs (i’ve check the PHP error log) that make it’s hard to find out the problem.
At the moment, we still take a look on this problem. It may take more time and for the meantime, you need to disable several option panels on the customizer because they will work fine when loading less option. In this case, you just need to edit this file /jnews/class/Customizer.php and jump into line 126. There is a list of option panels on the customizer. You just need to disable several of them that you don’t use.
Sorry for this inconvenience and let me know if you have further question.