Kyma Advanced theme edit

Hi.
I’m having a issue, here, I can’t edit my code.
When I tried to select Kyma Advanced theme to edit (from dashboard >> Appearance >> Theme Editor -> Select theme to edit)

I face error, it seems to be Page keep loading and finally got MAX TIME EXECUTION and show error like:

Server Connection Closed
Description: The server requested closed the connection before the transaction was completed.

I really need to edit, please help me solve, or let me know why this happens
Thank you.