Steps to reproduce:

1. Install Linux Maschine with Name "testmachine01.test.lds" with Zabbix Agent
2. Configure Maschine in Zabbix with Lower and Upper Case TESTMachine01.test.lds
3. Create Items for Machine with "Zabbix Agent (Active)" Checks and "Zabbix Agent" Checks

Result:

Zabbix Agent Checks are there

Zabbix Agent Active Checks are not displayed

Log File shows:

22554:20181030:045215.477 In recv_agenthistory()
22554:20181030:045215.477 In process_client_history_data()
22554:20181030:045215.477 In parse_history_data()
22554:20181030:045215.477 End of parse_history_data():SUCCEED processed:20/20
22554:20181030:045215.477 In process_history_data()
22554:20181030:045215.477 End of process_history_data() processed:0
22554:20181030:045215.477 End of process_client_history_data():SUCCEED
22554:20181030:045215.477 In zbx_send_response()
22554:20181030:045215.477 zbx_send_response() '{"response":"success","info":"processed: 0; failed: 20; total: 20; seconds spent: 0.000308"}'

Only in Debug Mode!
Expected:
Log File should show something like this, so we know that the configuration of the Server was wrong:

Machine TESTMachine01.test.lds not found for sending active Checks to Zabbix