Steps to reproduce:
1. Create a trapper text item and a trigger with a condition using this item:
Thus, we would like to fire this trigger when 3 last values of this item are not empty.
Based on https://www.zabbix.com/documentation/5.0/manual/appendix/triggers/functions, we can expect it, because:
⇒ strlen()(is equal to strlen(#1)) → length of the latest value
⇒ strlen(#3) → length of the third most recent value
2. Send 3 empty string to this item (just to collect enough data):
3. Send 1 non-empty string to this item:
The trigger was fired:
The trigger wasn't fired because the second and the third most recent values have empty string and their length is 0.