Problem with 3G dongle

I used a Buffalo WZR-HP-AG300H with a ZTE MF831 dongle for some years now.
Today I wanted to switch to a Netgear R7800. I got the internet connection running, but after every reboot i have to "save+apply" the WAN settings in the Interfaces section to enable the connection.

Anyone has the same problem? Which commands do luci execute when pressing save+apply?

Save +apply typically writes the configuration to the corresponding configuration file and then performs the configuration in /etc/config/ucitrack
Ucitrack may have the following

config network
	option init 'network'
	list affects 'dhcp'
	list affects 'radvd'

config wireless
	list affects 'network'

config firewall
	option init 'firewall'
	list affects 'luci-splash'
	list affects 'qos'
	list affects 'miniupnpd'

config olsr
	option init 'olsrd'

config dhcp
	option init 'dnsmasq'
	list affects 'odhcpd'

config odhcpd
	option init 'odhcpd'

config dropbear
	option init 'dropbear'

config httpd
	option init 'httpd'

config fstab
	option init 'fstab'

Thank you.
I think, that i solved it, with adding
/etc/init.d/network restart
to rc.local