Did the time of “10-May-2017 05:09:18” correspond to a time when you tried to save the masthead again? The messages from the error log will only be relevant if they come from the time when you tried to save the masthead.
Re-reading your initial report, I note you say “The save button start rotating for hours”. This raises the possibility that the error may simply be javascript related and not actually be touching the server. Open your web browser’s Web Inspector tool (usually accessed by F12), and use the Console tab to look for Javascript error messages. If the request goes to the server, you can also use the Network tab to see which request failed. Share those errors here.