Steps to reproduce:

1. Install Zabbix 5.4 on PostgreSQL 12 with TimescaleDB 1.7.5
2. Upgrade TimescaleDB to 2.x (2.6.0)
3. Upgrade PostgreSQL 12 to 13 (/usr/lib/postgresql/13/bin/pg_upgrade -b /usr/lib/postgresql/12/bin -B /usr/lib/postgresql/13/bin -d /var/lib/postgresql/12/main -D /var/lib/postgresql/13/main -o ' -c config_file=/etc/postgresql/12/main/postgresql.conf' -O ' -c config_file=/etc/postgresql/13/main/postgresql.conf')
4. Open Monitoring -> Hosts
5. Wait for an eternity as the query will take 100% CPU usage on PostgreSQL without result.

Result:

1. Query stuck: 

   SELECT DISTINCT t.triggerid FROM triggers t,functions f,items i WHERE i.hostid IN (16018,16138,16169,16181,16197,16199,16200,16213,16219,16223,16229,16233,16242,16271,16284,16291,16292,16305,16308,16310,16312,16319,16320,16328,16331,16332,16334,16340,16345,16370,16376,16384,16392,16402,16416,16423,16431,16458,16460,16470,16474,16475,16486,16489,16490,16491,16492,16493,16494,16496) AND f.triggerid=t.triggerid AND f.itemid=i.itemid AND NOT EXISTS (SELECT NULL FROM functions f,items i,hosts h WHERE t.triggerid=f.triggerid AND f.itemid=i.itemid AND i.hostid=h.hostid AND (i.status<>0 OR h.status<>0)) AND t.status=0 AND t.flags IN (0,4)

Expected:
See hosts overview