TL-WR810N - No access if booted without lan cable connected

Tp-Llink wr810N ver. 1.1
Openwrt ver. 17.04, 17.06, 18.06.0

After a fresh install...Everything is ok if the router boots with a lan cable connected to the computer (or if I connect the router wan to lan with the same cable).
I can disconnect it and connect later (or access by wifi if set) on But if the cable isn't pluged in when the router boots, it becomes inaccessible on ssh or http. Ip6 is set, but ip4 is missing... Nmap can't determine route to 192.168... Can't access logs... If I turn the wireless on, it connects but doesn't work (no ip4).
I tried to restart some services after boot by adding sth to the crontab, but it didn't help.

*/2 * * * * /etc/init.d/odhcpd restart && /etc/init.d/dropbear restart && /etc/init.d/firewall restart && /etc/init.d/dsnmasq restart

Any suggestions ? My Tp-link 1043ND is not affected.

The default IP after flashing is The default gateway IP adress is not set. It took me a week to identify the trigger... This bug can be repeated regardless of settings of the router's ip. No LAN connected on boot - no DHCP working on LAN/wifi and this device is useless. Is serves me as AP with 4G USB modem, so connecting wan to LAN solves the problem... but looks funny...