Steps to reproduce:

1. Changes in configuration /etc/zabbix/zabbix_server.conf:
   StartReportWriters=1
   WebServiceURL=http://localhost:10053/report
2. Stop zabbix-server

Result:

1. Zabbix-server log has a lot of records like
   update trends set num=41,value_min=52,value_avg=55.878048780487809,value_max=59 where itemid=27341 and clock=1621051200;
   update trends set num=42,value_min=0,value_avg=0,value_max=0 where itemid=27371 and clock=1621051200;
   update trends set num=41,value_min=0,value_avg=0,value_max=0 where itemid=24948 and clock=1621051200;
   update trends set num=42,value_min=0,value_avg=0,value_max=0 where itemid=24545 and clock=1621051200;
   update trends set num=42,value_min=99.072913999999997,value_avg=99.483465809523793,value_max=99.783007999999995 where itemid=26343 and clock=1621051200;
   update trends set num=41,value_min=0,value_avg=0,value_max=0 where itemid=25599 and clock=1621051200;
   update trends set num=41,value_min=0,value_avg=0,value_max=0 where itemid=25433 and clock=1621051200;
   update trends set num=41,value_min=55,value_avg=58.804878048780488,value_max=63 where itemid=27338 and clock=1621051200;
2. postgres zabbix zabbix UPDATE process eats memory (RAM+SWAP) until OOM takes place
3. after that postgres fails with 'FATAL: the database system is in recovery mode' messages
4. Deactivating StartReportWriters or WebServiceURL lead to normal working.

Expected:
Zabbix server start/stops normally of StartReportWriters and WebServiceURL are active.