Hi, sory about my english not well.
I confirm this problem, when i use transparent proxy for a week, problem start, time for loading a webpage too slow (about 20s). Next, i'm test with bypass http proxy for my local subnet (or IP), it going to normal. I think problem here is DNS response time and Squid, emty for /var/log/squid/squid.out,
tail -n 60 /var/log/messages:
root@Firewall:~ # tail -n 60 /var/log/messages
Oct 6 16:26:21 Firewall p3scan[7654]: Real-server address is 210.245.87.22:110
Oct 6 16:26:21 Firewall p3scan[7654]: USER '(null)'
Oct 6 16:26:21 Firewall p3scan[7654]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:26:34 Firewall p3scan[7663]: POP3 Connection from 192.168.170.55:4530
Oct 6 16:26:34 Firewall p3scan[7663]: Real-server address is 210.245.87.22:110
Oct 6 16:26:34 Firewall p3scan[7663]: USER 'Dealer20@thuylinh.com.vn'
Oct 6 16:26:34 Firewall p3scan[7663]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:26:38 Firewall p3scan[7664]: POP3 Connection from 192.168.170.45:48515
Oct 6 16:26:38 Firewall p3scan[7664]: Real-server address is 210.245.87.22:110
Oct 6 16:26:38 Firewall p3scan[7664]: USER '(null)'
Oct 6 16:26:39 Firewall p3scan[7664]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:26:41 Firewall p3scan[7666]: POP3 Connection from 192.168.170.47:2296
Oct 6 16:26:41 Firewall p3scan[7666]: Real-server address is 210.245.87.22:110
Oct 6 16:26:41 Firewall p3scan[7666]: USER 'dealer03@thuylinh.com.vn'
Oct 6 16:26:41 Firewall p3scan[7666]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:26:53 Firewall p3scan[7669]: POP3 Connection from 192.168.170.56:50115
Oct 6 16:26:53 Firewall p3scan[7669]: Real-server address is 210.245.87.22:110
Oct 6 16:26:53 Firewall p3scan[7669]: USER 'dealer29@thuylinh.com.vn'
Oct 6 16:26:53 Firewall p3scan[7669]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:00 Firewall sshd[7670]: Accepted password for root from ::ffff:192.168.170.253 port 41090 ssh2
Oct 6 16:27:00 Firewall sshd(pam_unix)[7670]: session opened for user root by (uid=0)
Oct 6 16:27:01 Firewall mailfile[7678]: Mail sent to 'network@thuylinh.com.vn'. Mail caller: 'EFW-20200018'
Oct 6 16:27:16 Firewall p3scan[7703]: POP3 Connection from 192.168.170.44:57386
Oct 6 16:27:16 Firewall p3scan[7703]: Real-server address is 210.245.87.22:110
Oct 6 16:27:17 Firewall p3scan[7703]: USER '(null)'
Oct 6 16:27:17 Firewall p3scan[7703]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:20 Firewall p3scan[7707]: POP3 Connection from 192.168.170.53:62005
Oct 6 16:27:20 Firewall p3scan[7707]: Real-server address is 210.245.87.22:110
Oct 6 16:27:20 Firewall p3scan[7707]: USER 'dealer18@thuylinh.com.vn'
Oct 6 16:27:20 Firewall p3scan[7707]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:21 Firewall p3scan[7708]: POP3 Connection from 192.168.170.58:41571
Oct 6 16:27:21 Firewall p3scan[7708]: Real-server address is 210.245.87.22:110
Oct 6 16:27:21 Firewall p3scan[7708]: USER '(null)'
Oct 6 16:27:21 Firewall p3scan[7708]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:34 Firewall p3scan[7710]: POP3 Connection from 192.168.170.55:4539
Oct 6 16:27:34 Firewall p3scan[7710]: Real-server address is 210.245.87.22:110
Oct 6 16:27:34 Firewall p3scan[7710]: USER 'Dealer20@thuylinh.com.vn'
Oct 6 16:27:34 Firewall p3scan[7710]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:38 Firewall p3scan[7712]: POP3 Connection from 192.168.170.45:48516
Oct 6 16:27:38 Firewall p3scan[7712]: Real-server address is 210.245.87.22:110
Oct 6 16:27:38 Firewall p3scan[7712]: USER '(null)'
Oct 6 16:27:39 Firewall p3scan[7712]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:41 Firewall p3scan[7713]: POP3 Connection from 192.168.170.47:2299
Oct 6 16:27:41 Firewall p3scan[7713]: Real-server address is 210.245.87.22:110
Oct 6 16:27:41 Firewall p3scan[7713]: USER 'dealer03@thuylinh.com.vn'
Oct 6 16:27:43 Firewall p3scan[7713]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:27:53 Firewall p3scan[7716]: POP3 Connection from 192.168.170.56:50117
Oct 6 16:27:53 Firewall p3scan[7716]: Real-server address is 210.245.87.22:110
Oct 6 16:27:53 Firewall p3scan[7716]: USER 'dealer29@thuylinh.com.vn'
Oct 6 16:27:54 Firewall p3scan[7716]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:28:16 Firewall p3scan[7734]: POP3 Connection from 192.168.170.44:57387
Oct 6 16:28:16 Firewall p3scan[7734]: Real-server address is 210.245.87.22:110
Oct 6 16:28:17 Firewall p3scan[7734]: USER '(null)'
Oct 6 16:28:17 Firewall p3scan[7734]: Session done (Clean Exit). Mails: 0 Bytes: 0
Oct 6 16:28:20 Firewall p3scan[7735]: POP3 Connection from 192.168.170.53:62011
Oct 6 16:28:20 Firewall p3scan[7735]: Real-server address is 210.245.87.22:110
Oct 6 16:28:21 Firewall p3scan[7738]: POP3 Connection from 192.168.170.58:59659
Oct 6 16:28:21 Firewall p3scan[7738]: Real-server address is 210.245.87.22:110
Oct 6 16:28:21 Firewall p3scan[7738]: USER '(null)'
Oct 6 16:28:21 Firewall p3scan[7738]: Session done (Clean Exit). Mails: 0 Bytes: 0
cat /var/log/messages | grep -i error = nothing
and don't know how to resolve. Hope for answer!