The re-open functionality leverages bug_update.php but gets access denied for reporters because it trips over the following check:

reporter doesn't have update access.

access_ensure_bug_level( config_get( 'update_bug_threshold' ), $f_bug_id );

When re-opening an issue, it is going from readonly to read-write.

Hence, this check will fail.

if( bug_is_readonly( $f_bug_id ) ) {
error_parameters( $f_bug_id );
trigger_error( ERROR_BUG_READ_ONLY_ACTION_DENIED, ERROR );
}

The update_bug_status_threshold here is redundant and trips reporters.

if( $t_existing_bug->status !== $t_updated_bug->status ) {
access_ensure_bug_level( config_get( 'update_bug_status_threshold' ), $f_bug_id );

This check will not allow re-opening closed issued. It should check for >= $t_resolved_status

and <= $t_closed_status

$t_reopen_issue &&
$t_existing_bug->status < $t_closed_status &&

$t_existing_bug->view_state is of type string, needs to be casted to (int).

if( $t_existing_bug->view_state !== $t_updated_bug->view_state ) {