get_the_excerpt breaking wp-json API

[DannyCooper]

When creating a dynamic block for Gutenberg I added this code to a plugin:

register_block_type( 'my-plugin/latest-post', array(
	'render_callback' => 'my_plugin_render_block_latest_posts',
) );

function my_plugin_render_block_latest_posts( $atts ) {

	$output = '';

	$args = array(
		'posts_per_page' => 3,
	);

	$query = new WP_Query( $args );

	if ( $query->have_posts() ) :
		while ( $query->have_posts() ) :
			$query->the_post();
			$output .= '<li>';
			$output .= get_the_excerpt();
			$output .= '</li>';
		endwhile;
		wp_reset_postdata();
	else :
		$output .= 'No posts found.';
	endif;

	return $output;
}

For some reason, get_the_excerpt is causing this error in /wp-json/wp/v2/posts:

Fatal error: Maximum function nesting level of '256' reached, aborting! in /app/public/wp-includes/plugin.php on line <i>899</i>

When I remove get_the_excerpt() or replace it with get_the_content() the error disappears.

I use 'Local by Flywheel' and this is happening on PHP5.6 and 7