Finish a column

An easy way to do that is keep adding 4 fields for columns, but you can use a special field like custom_html with zero content. That forces the plugin to output empty divs in the column which helps to maintain the layout.

It does have clear floats, of course. But the thing is the plugin needs correct number of columns to output correct opening and closing divs. You can see it in the console like this:

Here is an example to illustrate what I meant in previous reply: assuming we have 2 rows, 1st row has 2 fields (each field has 1/4 width), 2nd row has 4 fields (each field has 1/4 width):

add_filter( 'rwmb_meta_boxes', function ()
{
	return [
		[
			'title'  => 'Demo columns',
			'fields' => [
				[
					'id'      => 'text1',
					'type'    => 'text',
					'name'    => 'Text1',
					'columns' => 3,
				],
				[
					'id'      => 'text2',
					'type'    => 'text',
					'name'    => 'Text2',
					'columns' => 3,
				],
				[
					'type'    => 'custom_html',
					'std' => '',
					'columns' => 6,
				],
				[
					'id'      => 'text5',
					'type'    => 'text',
					'name'    => 'Text5',
					'columns' => 3,
				],
				[
					'id'      => 'text6',
					'type'    => 'text',
					'name'    => 'Text6',
					'columns' => 3,
				],
				[
					'id'      => 'text7',
					'type'    => 'text',
					'name'    => 'Text7',
					'columns' => 3,
				],
				[
					'id'      => 'text8',
					'type'    => 'text',
					'name'    => 'Text8',
					'columns' => 3,
				],
			],
		]
	];
} );