Hi there,
I’m getting this warning on global blocks on multiple sites:
The preview could not load due to the iframe response being incomplete. This is most often related to a plugin conflict, or customizations introducing a PHP error.
From trying to deactivate plugins it seems SEO Press Pro is the culprit (not their base plugin but the pro add on.
I’m just deactivating it to do edits at the moment but thought I’d flag it, noticed it on 3 sites today.