bbPress.org

Common thing to see if you activated tinymce for bbPress. Some of the html tags bbPress restricts usage from regular participants could also be used for Tinymce. Customize this function to your liking if there are many more html tags not outputting.

add_filter( 'bbp_kses_allowed_tags', 'ntwb_bbpress_custom_kses_allowed_tags' );
function ntwb_bbpress_custom_kses_allowed_tags() {
	return array(
		// Links
		'a'          => array(
			'class'    => true,
			'href'     => true,
			'title'    => true,
			'rel'      => true,
			'class'    => true,
			'target'    => true,
		),
		// Quotes
		'blockquote' => array(
			'cite'     => true,
		),
		
		// Div
		'div' => array(
			'class'     => true,
		),
		
		// Span
		'span'             => array(
			'class'     => true,
                        'style'     => true,
		),
		
                // Paragraph
		'p'             => array(
			'class'     => true,
                        'style'     => true,
		),

		// Code
		'code'       => array(),
		'pre'        => array(
			'class'  => true,
		),
		// Formatting
		'em'         => array(),
		'strong'     => array(),
		'del'        => array(
			'datetime' => true,
		),
		// Lists
		'ul'         => array(),
		'ol'         => array(
			'start'    => true,
		),
		'li'         => array(),
		// Images
		'img'        => array(
			'class'    => true,
			'src'      => true,
			'border'   => true,
			'alt'      => true,
			'height'   => true,
			'width'    => true,
		),
		// Tables
		'table'      => array(
			'align'    => true,
			'bgcolor'  => true,
			'border'   => true,
		),
		'tbody'      => array(
			'align'    => true,
			'valign'   => true,
		),
		'td'         => array(
			'align'    => true,
			'valign'   => true,
		),
		'tfoot'      => array(
			'align'    => true,
			'valign'   => true,
		),
		'th'         => array(
			'align'    => true,
			'valign'   => true,
		),
		'thead'      => array(
			'align'    => true,
			'valign'   => true,
		),
		'tr'         => array(
			'align'    => true,
			'valign'   => true,
		)
	);
}

You may not need to completely turn off the html editor tab now, as it is quite useful for users.