SYN packets are not seen at destination (sp: 10802 dp : 443-https)

Hi

 

I have a strange situation. Two customers: Without any change the customer A with ip a.a.a.a port 10802 is no more able to communicate with ip address b.b.b.b port 443 (customer B).

 

The customer range is behind F5 and Customer A is not behind F5. Previous week ago, the communication between both ip was well.

 

The other ip addresses in the same range are routed correctly. During issue the Customer A tried to sent SYN packet to Customer B and those SYN packets were not seen at destination.

 

On F5, no drop was seen.

 

In the same time we decided to upgrade firmware. Now we are using version BIG-IP 12.1.3.7

 

Then per miracles, everything work now correctly. The only thing we had done is the upgrade.

 

My question is to now what could justify this strange behaviour. Do you know eventual bug for the port 443 ?

 

Thank four for your suggestions/ help.