Agent active check process sending buffered data periodically, but some case data sending is delayed:

• log, logrt, eventlog key without skip option, and after restarting agent
• system.run or user parameter with active check with large timeout

because send_buffer called after all active check items are processed, and agent has only one active check process.

For example:

• active check item A store value Z in buffer
• only one value on buffer, not sending
• active check item B start to process then timeout with 30 sec
• after processing item B, agent send value Z to server

This case Zabbix server received the value with 30 sec delay. There's a possibility that triggers with timer based function create incorrect events in this case.