Steps to reproduce:

1. Create user_parameter key on /etc/zabbix/zabbix_agent2.d/test.conf or /etc/zabbix/zabbix_agent2.conf
2. Run zabbix_agent2 -p

Result:
Custom key does not show up on output

Key can be tested perfectly using zabbix_agent2 -t test.item

Specifying the config using -c does not change result
Expected:
Custom key to show up.

Same config does work on zabbix_agentd

See attachment test