Go step by step and test.
1. Click in the menu bar and click Force Quit.
Launch Safari holding the shift key down.
2. If Safari is slow, stops responding, quits unexpectedly, or has other issues
Section: Manage Extensions
3. Enable Develop menu and Empty Caches
4. Remove cookies and website data.
Manage cookies and website data:
5. Sometimes third party software can cause this kind of a problem.
Please run EtreCheck and post the report here.
Download it, open Downloads folder, click on it to open and select ”Open”.
Select a problem from the “Choose a problem” popup menu box, and then “Start EtreCheck” in the dialog.
Click “Share Report” button in the toolbar, select “Copy to Clipboard”, and then paste it when you reply.