Hosting Migration Issues

After some recent access issues to my site, I have switched hosting providers. I have tried to move my site across using a WP plugin called All-in-one-WP-migration, which I have used several time successfully and with no issues. However, this time I'm having massive problems, and I think it has something to do with the upfront system.

I have attached a screenshot showing the issues:
When I try to open up the website it used to look like the image on the left, now it looks like the image on the right. When I open the page using Upfront, it renders correctly and I see the page as it should be, so I try to save it to try and force the correct version through but I get the error as shown.

Can anyone tell me what I'm doing wrong / how I might fix it?

Thanks!