wrong number for speed in /usr/local/www/services_ntpd_gps.php
$section->addInput(new Form_Select( 'gpsspeed', null, $pconfig['speed'], [0 => '4800', 15 => '9600', 32 => '19200', 48 => '38400', 64 => '57600', 80 => '115200'] ))->setHelp('A higher baud rate is generally only helpful if the GPS is sending too many sentences. ' . 'It is recommended to configure the GPS to send only one sentence at a baud rate of 4800 or 9600.');
The number for 9600 baud speed should be 16! Now you get wrong mode in generated ntpd.conf.
See also: https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html