Go step by step and test.
1. Delete Cookies
Safari > Preferences > Privacy > Cookies and other website data:
Click the “Details” button.
Remove all cookies except from Apple, your internet service provider and banks.
2. Safari > Preferences > Extensions
Turn off Extensions if any and launch Safari again to test.
Turn on those one by one and test.
3. Delete Caches.db
Close all windows and quit all applications.
Hold "option" key down and click "Go" menu in the Finder menu bar.
Select "Library" from the dropdown.
Library > Caches > com.apple.Safari > Caches.db
Right click the Caches.db file and select "Move To Trash.
Close windows and relaunch Safari.
4. Empty Caches
Safari > Preference > Advanced
Checkmark the box for "Show Develop menu in menu bar".
Develop menu will appear in the Safari menu bar.
Click Develop and select "Empty Caches" from the dropdown.
5. Temporarily turn off Safari iCloud sync and test.
System Preferences > iCloud
Uncheck the box beside “Safari” and test.