Pre-problem:
I upgraded Zabbix 3.2.4rc1 (revision 65645) to 3.2.5rc1 (revision 66325). Because 3.2.4 is working fine for everyone else, I can assume problem introduced somewhere between 3.2.4 (r65975) and 3.2.5rc1 (r66325).

Problem itself:
Following trigger was not fired for 5 days after upgrade, but was working before:

({TRIGGER.VALUE}=0 and {host:system.cpu.util[,idle,avg15].avg(30m)}<30) or ({TRIGGER.VALUE}=1 and  {host:system.cpu.util[,idle,avg15].avg(30m)}<30 + 1)

History of values clearly shows values all lower than threshold (30) for a few hours. Trigger configuration screenshot in attachment.