F5 LTM and Sharepoint

Port congestion would be based on unique source IP addresses, and could happen if you're SNATting traffic with a single auto-map self-IP. Do you have a monitor on the pools? What kind of failure are you seeing? No access to SharePoint at all or some limit the access as if there was no access to the database? If the former, when it fails, open a shell on the F5 and see if you can access the server (ping, curl).