TCP issues after Proxmox upgrade from 1.9 to 2.1

[Scott A. Marlin]

I just did the upgrade from 1.9 to 2.1 and now we are having seemingly random TCP connection issues.
While most users access network resources without any problem, others are experiencing timeouts on various services such as proxy, http, smtp, etc.
Tcpdump shows that the TCP SYN packets are going unanswered.
Any ideas ?

Thank you in advance.

15:39:07.570651 IP 192.168.10.63.1569 > proxycache.acc.fr.8000: Flags , seq 145971721, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:07.571378 IP 192.168.10.63.1570 > proxycache.acc.fr.8000: Flags , seq 3466339044, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:07.820025 IP 192.168.10.63.1571 > proxycache.acc.fr.8000: Flags , seq 1194764556, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:09.769316 IP 192.168.10.63.1572 > proxycache.acc.fr.8000: Flags , seq 4073948366, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:10.019567 IP 192.168.10.63.1573 > proxycache.acc.fr.8000: Flags , seq 1315289603, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:10.492691 IP 192.168.10.63.1569 > proxycache.acc.fr.8000: Flags , seq 145971721, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:10.495216 IP 192.168.10.63.1570 > proxycache.acc.fr.8000: Flags , seq 3466339044, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:10.786651 IP 192.168.10.63.1571 > proxycache.acc.fr.8000: Flags , seq 1194764556, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:11.764396 IP 192.168.10.63.1574 > proxycache.acc.fr.8000: Flags , seq 3022547923, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:11.764569 IP 192.168.10.63.1575 > proxycache.acc.fr.8000: Flags , seq 1550074840, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:11.765143 IP 192.168.10.63.1576 > proxycache.acc.fr.8000: Flags , seq 1786371980, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:12.013761 IP 192.168.10.63.1577 > proxycache.acc.fr.8000: Flags , seq 1108366855, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:12.014028 IP 192.168.10.63.1578 > proxycache.acc.fr.8000: Flags , seq 1367931683, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:12.015517 IP 192.168.10.63.1579 > proxycache.acc.fr.8000: Flags , seq 2283504113, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:12.690988 IP 192.168.10.63.1572 > proxycache.acc.fr.8000: Flags , seq 4073948366, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0
15:39:12.990847 IP 192.168.10.63.1573 > proxycache.acc.fr.8000: Flags , seq 1315289603, win 65535, options [mss 1460,nop,wscale 1,nop,nop,TS val 0 ecr 0,nop,nop,sackOK], length 0