Hello, Tom
If you are still experiencing the same issue even when the default theme is activated, it means that the issue does not depend on the theme, so unfortunately our Theme Support team cannot help you with this.
It is possible that your hosting provider or WordPress support service may be able to provide you with a solution to your problem.
We can only assist in cases where the issue is directly caused by our theme.
We hope for your understanding.
Kind Regards,
8Themes Team