Added some logging:
Sep 20 19:42:05 php-fpm 318 /rc.newwanip: CALL sigkillbypid( /var/run/dpinger_OPT2_DHCP~100.64.240.50~8.8.4.4.pid ) [ simplestacktrace2(..) - /etc/inc/util.inc:69 sigkillbypid(..) - /etc/inc/util.inc:32 killbypid(..) - /etc/inc/gwlb.inc:85 stop_dpinger(..) - /etc/inc/gwlb.inc:301 setup_gateways_monitor(..) - /etc/rc.newwanip:195 ]
Sep 20 19:42:05 php-fpm 318 /rc.newwanip: CALL sigkillbypid( /var/run/dpinger_WAN_DHCP~100.64.143.98~8.8.8.8.pid ) [ simplestacktrace2(..) - /etc/inc/util.inc:69 sigkillbypid(..) - /etc/inc/util.inc:32 killbypid(..) - /etc/inc/gwlb.inc:85 stop_dpinger(..) - /etc/inc/gwlb.inc:301 setup_gateways_monitor(..) - /etc/rc.newwanip:195 ]
Sep 20 19:42:05 php-fpm 318 /rc.newwanip: CALL sigkillbypid( /var/run/dpinger_WAN_DHCP~100.64.143.98~8.8.8.8.pid ) [ simplestacktrace2(..) - /etc/inc/util.inc:69 sigkillbypid(..) - /etc/inc/util.inc:32 killbypid(..) - /etc/inc/gwlb.inc:85 stop_dpinger(..) - /etc/inc/gwlb.inc:166 start_dpinger(..) - /etc/inc/gwlb.inc:309 setup_gateways_monitor(..) - /etc/rc.newwanip:195 ]
Sep 20 19:42:05 php-fpm 318 /rc.newwanip: CALL start DPINGER( 8.8.8.8 ) [ simplestacktrace(..) - /etc/inc/gwlb.inc:181 start_dpinger(..) - /etc/inc/gwlb.inc:309 setup_gateways_monitor(..) - /etc/rc.newwanip:195 ] 0
Sep 20 19:42:05 php-fpm 318 /rc.newwanip: CALL sigkillbypid( /var/run/dpinger_OPT2_DHCP~100.64.240.50~8.8.4.4.pid ) [ simplestacktrace2(..) - /etc/inc/util.inc:69 sigkillbypid(..) - /etc/inc/util.inc:32 killbypid(..) - /etc/inc/gwlb.inc:85 stop_dpinger(..) - /etc/inc/gwlb.inc:166 start_dpinger(..) - /etc/inc/gwlb.inc:309 setup_gateways_monitor(..) - /etc/rc.newwanip:195 ]
Sep 20 19:42:05 php-fpm 318 /rc.newwanip: CALL start DPINGER( 8.8.4.4 ) [ simplestacktrace(..) - /etc/inc/gwlb.inc:181 start_dpinger(..) - /etc/inc/gwlb.inc:309 setup_gateways_monitor(..) - /etc/rc.newwanip:195 ] 0
And it looks like dpinger is being killed and immediately started again, i suspect the old process is still 'shutting down'.. And deletes the pid file as a final step, while actually the new dpinger was already running..