Sharepoint Refused to Connect suddenly on SmartSheet

Hi all,

We use SmartSheet Apps and have a few SharePoint Site pages displaying in SmartSheet which use an iFrame.

Suddenly all those iFrame pages now refuse to display the SharePoint pages "SharePoint.com refused to connect". 

The headers in the SharePoint site, the X-Frame, is set to SAMEDOMAIN which is causing the problem. We cannot see how we can change this or why it has suddenly changed so the external iFrame cannot connect?

We have reached out to SmartSheet support and they have confirmed that it is our SharePoint site that is the problem. We have tried to change the HTML Field settings to allow any site, but I think that is to allow content to iframe in SharePoint, but changed it nethertheless.

Could I please ask if someone knows how a SharePoint site would change in the X-Frame value? It is a SharePoint Online site and not on-Prem.

Thank you in advance

Jason