Removing #markup may cause errors or unexpected behaviours on websites

In version 8.x-1.2 the #markup element is removed

$element[$delta] = array('#markup' => $output);

and replaced for

$element[$delta] = [
        '#type' => 'processed_text',
        '#text' => $output,
        '#format' => $item->format,
];

We did some checks to see if #markup was filled, but because that element did not exist anymore in the array we had an unexpected error. Maybe next time add some more info in the Release notes, because when you read them right now, you don't expect code changes like this.

I don't know in what category this fits, but I hope people can find this issue when they have the same problem.