On the ASUS RT-AC51U does not work wifi 2,4 GHz

The 2.4 GHz wifi is unable to assign an IP address, nor did the static assignment of the IP address help.

In system log IP is assign DHCP:

Sun Feb  9 17:22:45 2020 daemon.info hostapd: wlan1: STA 70:4d:7b:80:40:46 IEEE 802.11: authenticated
Sun Feb  9 17:22:45 2020 daemon.info hostapd: wlan1: STA 70:4d:7b:80:40:46 IEEE 802.11: associated (aid 2)
Sun Feb  9 17:22:45 2020 daemon.notice hostapd: wlan1: AP-STA-CONNECTED 70:4d:7b:80:40:46
Sun Feb  9 17:22:45 2020 daemon.info hostapd: wlan1: STA 70:4d:7b:80:40:46 WPA: pairwise key handshake completed (RSN)
Sun Feb  9 17:23:22 2020 daemon.notice hostapd: wlan1: AP-STA-DISCONNECTED 70:4d:7b:80:40:46

IP is static

Sun Feb  9 17:48:46 2020 daemon.info hostapd: wlan1: STA 70:28:8b:ad:b7:07 IEEE 802.11: authenticated
Sun Feb  9 17:48:46 2020 daemon.info hostapd: wlan1: STA 70:28:8b:ad:b7:07 IEEE 802.11: associated (aid 2)
Sun Feb  9 17:48:46 2020 daemon.notice hostapd: wlan1: AP-STA-CONNECTED 70:28:8b:ad:b7:07
Sun Feb  9 17:48:46 2020 daemon.info hostapd: wlan1: STA 70:28:8b:ad:b7:07 WPA: pairwise key handshake completed (RSN)

In the "Status" "Associated Stations" is phone visible with the right IP, but not function.
In the phone the assignment IP cycle is repeated over and over.
It happens on all our phones.

Thank you in advance for advice on what to do.

first you should mentioned wich fw you have in this chinese electronic magic box?stock asus merlin or certain openwrt version?

I have latest fw OpenWrt 19.07.1

And the router is HW Ver.:A

It seems to be working fine for me, when I've created a second network on the bgn (second) adapter. Sorry if I'm not clear, I'm a complete noob...