Download template "Template DB PostgreSQL agent 2" from the official git: Source of template_db_postgresql_agent2.xml - Zabbix - ZABBIX GIT

Import it in your Zabbix environment and see how item "PostgreSQL: Cache hit" breaks due to missing parameters:

pgsql.cache.hit["{$PG.URI}"]

It is missing {$PG.USER} and {$PG.PASSWORD} user parameters in the key.

Expected:

pgsql.cache.hit["{$PG.URI}","{$PG.USER}","{$PG.PASSWORD}"]

Easy but important fix.