Hi,
From the screenshots it looks like as if the server was overloaded, and it does not respond. The most likely cause is usually low memory – it is especially true in cases where too many plugins are active and the server can no longer handle that. Another possibility is a 3rd party conflict, it is very rare, but still can happen.
Do you have any error logs by any chance? I am more than happy to investigate.
Can you please also add temporary back-end and FTP access? I will try to debug through the save process to see what exactly triggers the issue.