TCP connection hangs occasionally sending multiple Syn requests

Issue

1) When it's normal status, TCP connections works well with normal follow SYN -> SYN-ACK <- ACK

14:27:54.499057 IP hosta.xxx > hostsb.yyy: S 2006245217:2006245217(0) win 5840 <mss 1460,sackOK,timestamp 1597686371 0,nop,wscale 7>
14:27:54.499705 IP hostsb.yyy > hosta.xxx: S 591760326:591760326(0) ack 2006245218 win 65535 <mss 1460,nop,wscale 3,sackOK,timestamp 802655622 1597686371>
14:27:54.499736 IP hosta.xxx > hostsb.yyy: . ack 1 win 46 <nop,nop,timestamp 1597686372 802655622>

2) But when there's a problem and the connection hangs, only SYN packets have been sent but no corresponding SYN ACK response can be seen on the wire.

14:29:14.375334 IP hostc.xxx > hostc.yyy: S 2074497474:2074497474(0) win 5840 <mss 1460,sackOK,timestamp 1597766247 0,nop,wscale 7>
14:29:17.375815 IP hostc.xxx > hostc.yyy: S 2074497474:2074497474(0) win 5840 <mss 1460,sackOK,timestamp 1597769247 0,nop,wscale 7>
14:29:23.375694 IP hostc.xxx > hostc.yyy: S 2074497474:2074497474(0) win 5840 <mss 1460,sackOK,timestamp 1597775247 0,nop,wscale 7>
14:29:35.375469 IP hostc.xxx > hostc.yyy: S 2074497474:2074497474(0) win 5840 <mss 1460,sackOK,timestamp 1597787247 0,nop,wscale 7>
14:29:59.375989 IP hostc.xxx > hostc.yyy: S 2074497474:2074497474(0) win 5840 <mss 1460,sackOK,timestamp 1597811247 0,nop,wscale 7>

• Application reports connection timeout