Go step by step and test.
1. Click in the menu bar and choose “Force Quit”.
In the window that opens up, select “Safari” and click “Force Quit.
Relaunch Safari holding the shift key down.
2. Empty Caches and test.
Safari > Preference > Advanced
Checkmark the box beside "Show Develop menu in menu bar".
Develop menu will appear in the Safari menu bar.
Click Develop and select "Empty Caches" from the dropdown.
3. Disable Extensions and test.
Safari > Preferences > Extensions
Select, disable all extensions and test.
Enable Extensions one by one and test.
To uninstall any extension, select it and click the “Uninstall” button.