Reassembling TCP PDU

Hi O_Muz , 
What I have got from your environment , you have some issues with Fragmentation resulted from variance in MTUs Values in Client side peers , Also " TCP Zero Window " sometimes indicates there is a peer sends traffic with a rate higher than the oppsite peer. 
So maybe adjusting MTU value from F5 Loadbalancer or SD-WAN tunnels " to make their MTUs Value identical " should solve this issue. 

> in Case you are using SNAT listners , you can adjust MTU value for external Vlan , I mean the Vlan which " SNAT Listner " operates or listnes to client traffic , such as below : 


- Try to adjust it to match with your MSS/MTU SD-WAN tunnel value , and check again. 

If you use the Full proxy architecture with Virtual servers as a listeners , Check below : 
 
> I recommend to create a custom TCP profile for the Client side and adjust the MSS value as below snap shot: 

and attach this Profile in " Protocol Profile (client) " in your targeted virtual server which serves your application , and do not forget to assign another TCP profile in " protocol Profile (server) ". 

I hope my reply helps you