Hi, I'm Ashik. Welcome to JustAnswer. I'm reviewing your question now, and will post back with your reply ASAP
It could be old website data causing the problem. We can reset Safari and see if it works or not.
Click on Safari menu and select Clear History and Website Data. On the drop down next to Clear, select All History and click Clear History.
(If you see Reset Safari instead, click it and Reset Safari)
Check Gmail. Please let me know if that didn't work, so we can continue troubleshooting