This may be cache or cookies issue. Try to reset Safari settings:
1.Open Safari
2. Click on Safari menu at the top(to the right from the Apple logo)
3. Select preferences/privacy tab
4. Click on Remove all website data
5. Close Safari.
Delete Safari cache files:
1. Click on finder
2. Look for GO menu at the top
3. click on GO and hold down the option key. This will show user library folder.
4. Click on Library and look for Caches folder
5. In caches folder open com.apple.Safari folder
6. Move to trash Cache.db file.
This should solve the issue. If it will not help try to turn off Safari extentions
1.Open Safari
2. Click on Safari menu at the top(to the right from the Apple logo)
3. Select preferences
4. Find extentions tab
5. Turn off all the extentions
6. Relauch Safari