SNMP Error: Timeout

Steps to reproduce:

I've set up recently a Zabbix 6.0 environment with which I want to monitor 8 computers in the same network with SNMPv3

I created a template with items and linked it to the hosts.

Result:

I see that only 2 of them are sending data to the Zabbix server. The others apper as "Not available" with the error "Timeout while connecting to x.x.x.x:161".

I deceided to check it on my own by sending requests (SNMPGET & SNMPWALK) per Terminal to the machines that theoretically are not available and received the data inmediately.

Expected:
As the machines are reachable per Terminal I checked once again that the authentification data I wrote in the configuration is right and indeed it is. So I guess the error is in the Zabbix environment.

How can I solve it?