Hi Mei,
If you have followed the export/import
folder structure, there should not be a problem.
The only problem I can think of is that you are using hosting provider - and probably during export of the site, some if the limits are exceeded - CPU or memory usage and the application is recycled by the system. So, it does not seem to be the problem in your code in App_Code folder. Could you please check the limits set by the provider?
Best Regards,
Juraj Ondrus