Upgraded our instance from 7.4.3 to 7.4.5 on 4.11.25, and a few days later noticed that trends were not being saved anymore. There were no other changes, nor any errors in zabbix server or postgres logs.

Reverted to 7.4.3 and trends started being populated again. Then installed 7.4.4 and the problem came back.

Only thing that comes to mind about our data is that we regularly have history values saved with clock in the future, but this never prevented trends from being generated.