whether F5 will allow traffic [Port 80 or 443] to pass through with same tcp seq number ??

it is like continuous traffic link SYN attack

Usually ISNs (Initial sequence numbers) are unique on the same host but another host may use the same sequence number. Also note that F5 is not affected by the below vulnerability:

Predictable TCP sequence numbers allow spoofing. (CVE-1999-0077) https://support.f5.com/csp/article/K16883