The problem is the same for n dashes, m dashes, and any other type of HTML entities. The issue is only occurring in the messages on the Messages summary page.
The snippet in the BP function that truncates the message and appends the list with the ellipsis is as follows:
function bp_create_excerpt( $text, $length = 225, $options = array() ) {
// Backward compatibility. The third argument used to be a boolean $filter_shortcodes.
$filter_shortcodes_default = is_bool( $options ) ? $options : true;
$r = bp_parse_args(
$options,
array(
'ending' => __( ' [U+02026] ' , 'buddypress' ),
'exact' => false,
'html' => true,
'filter_shortcodes' => $filter_shortcodes_default,
'strip_tags' => false,
'remove_links' => false,
),
'create_excerpt'
);