'maxwait' option, 3g modem

How work 'maxwait' option in 3g interface? The interface does not start after router reboot with "no_device" error (ifstatus) . For up interface i need "/etc/init.d/network restart && ifup modem".
If I add "sleep 2" in /etc/init.d/network script. After reboot everything is fine, modem connected, without network restart. My interface config:

config interface 'modem'
        option proto '3g'
        option delegate '0'
        option service 'umts'
        option apn 'internet'
        option ipv6 '0'
        option maxwait '20'
        option peerdns '0'
        option device '/dev/ttyUSB3'
        option dns '1.1.1.1 208.67.222.222 8.8.8.8'

So why network dont wait modem? That option doesn't work?

I have the same problem, using own image, built from TRUNK.
Modem is Quectel EC25.
According to logread, pppd is not started after boot.

Sat Aug 3 10:22:43 2019 daemon.notice netifd: wwan (1010): SIM ready
Sat Aug 3 10:22:43 2019 daemon.notice netifd: wwan (1010): PIN set successfully
Sat Aug 3 10:22:44 2019 daemon.err hostapd: Configuration file: /var/run/hostapd-phy0.conf
Sat Aug 3 10:22:46 2019 kern.info kernel: [ 34.409817] ieee80211 phy0: rt2800_rf_self_txdc_cal: Info - RF Tx self calibr
Sat Aug 3 10:22:46 2019 kern.info kernel: [ 34.410348] ieee80211 phy0: rt2800_rf_self_txdc_cal: Info - RF Tx self calibr
Sat Aug 3 10:22:46 2019 daemon.notice netifd: Interface 'wwan' is now down

/etc/init.d/network restart
from CLI finally starts 3g-wwan.