There is a negative duration issue that is described in the documentation: https://www.zabbix.com/documentation/current/manual/web_interface/frontend_sections/monitoring/problems. 

"When item data that resolve the problem event are sent by Zabbix sender and contain a timestamp earlier than the problem creation time.."

In our case, the arrival of data from the past is a fairly frequent event, and it is important for us that the trigger does not fire at all on old data, but only fires on data that came with the latest timestamp.

We need the same behavior of the last() function in the trigger expression as the behavior of the last() function in the calculated data items formula, i.e. getting the value of the data item that came last in time.