We've replaced the site.php file. This made no difference. We then upgraded to version 3.7.12 (from 3.7.1) and this removed the error message, but we still have a blank/white home page - similarly for some other webpages developed in SP Page Builder that were effected when this issue first arose. I'd be grateful if you could urgently advise next steps.
To confirm, I compared the two files and the difference were:
Was:
$output .= '<img class="sppb-img-responsive'.$image_strech.''.($placeholder ? ' sppb-element-lazy' : '').'" src="' . ($placeholder ? $placeholder : $image_link) . '" alt="'. $alt_text .'" '.($placeholder ? 'data-large="'.$image_link.'"' : '').' '.($image_width ? 'width="'.$image_width.'"' : '').' '.($image_height ? 'height="'.$image_height.'"' : '').' loading="lazy">';
Now:
$output .= '<img class="sppb-img-responsive'.$image_strech.''.($placeholder ? ' sppb-element-lazy' : '').'" src="' . ($placeholder ? $placeholder : is_string($image_link) ? $image_link : $image_link->src) . '" alt="'. $alt_text .'" '.($placeholder ? 'data-large="'.$image_link.'"' : '').' '.($image_width ? 'width="'.$image_width.'"' : '').' '.($image_height ? 'height="'.$image_height.'"' : '').' loading="lazy">';