Map Label network show unknown

[lcw321321]

My case:
zabbix 5.0
Ubuntu 18.04.5 LTS

Map's Label:

Host:{HOST.NAME}
IP:{HOST.IP}
OS:{{HOST.HOST}:system.uname.last(0)}
CPU Load:{{HOST.HOST}:system.cpu.load[all,avg5].last(0)}
Free memory:{{HOST.HOST}:vm.memory.size[pavailable].last(0)}
Incoming network:{{HOST.HOST}:net.if.in[em1].last(0)}

Show:
Host:My client server name
IP:my client IP
OS: Linux my servername 3.13...
CPU Load: 0.57
Free memory:40.123%
Incoming network:*UNKNOWN*

I used zabbix_get to test connection, it was working.

root@zabbix-server:~# zabbix_get -s clientIP -p 10050 -k "net.if.in[em1]"
1129036557129

root@myclient server:~# ifconfig

em1 Link encap:Ethernet HWaddr ac:**************
inet addr:**.**.**.** Bcast:**.**.**.** Mask:255.255.255.192
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:61949182305 errors:0 dropped:0 overruns:1135 frame:0
TX packets:34887522665 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:13432091445933 (13.4 TB) TX bytes:9572536070316 (9.5 TB)
Memory:df200000-df280000

How can I solve it? thanks very much,it is blocking me 2 weeks.