Yes this is most certainly an issue with your theme then.
To figure out what the error is (assumption is it’s a JavaScript error), right click anywhere on the page, and then select Inspect
This will open the developer tools window, click on the Console tab, and then refresh the page. You should see some type of error in red that probably gives a slight bit of detail as to what the error is.
You should then contact your theme developer for support and provide them with details as to the issue you’re having, plus anything you found in the console