zabbixproxy failed to connect to zabbixserver

[onlybee]

Zabbix proxy and zabbix server both run with postgresql.

I check in zabbix web->Configuration->proxies, the last seen is 1h ago.
In zabbixproxy log, it shows:
504:20211127:132822.717 cannot send heartbeat message to server at "zabbixserver": ZBX_TCP_READ() timed out
505:20211127:132858.097 cannot send proxy data to server at "zabbixserver": ZBX_TCP_READ() timed out


However, zabbix server works fine and no error log found in server log. And I confirmed the network communication between proxy and server is fine.
I checked the data in database, found large amount of data in table zabbixproxy.proxy_history:
zabbixproxya=> select count(*) from proxy_history;
count
---------
3724251
(1 row)


I tried to truncate the table:
zabbixproxya=> truncate table proxy_history;
TRUNCATE TABLE


As soon as the table is tuncated, the heartbeat sent from proxy to server successfull!
However, the data in table proxy_history kept growing while proxy data sent to zabbixserver successfully and after about 10 minutes, it growed to about 10M and zabbixproxy failed to connect to zabbixserver again.

Please help to find out what's wrong.