Iframe with embedded google site does not working anymore

I had several pages in my wpordpress site with embedded iframe to google sites. This was working great. Suddenly since one or two days these pages are empty….?
The google sites are sitll there. Is this a change in policy of Google?. Is there anybody who knows how to solve this problem?

In the meantime I solve this my self (i hope temporary) to use MyWindow=window.open and link to these googlesites.