Pool can not select pool member for POST from IE 11

Unless you are using oneconnect or LB:detach, a load balancing decision will only be triggered once per connection. So, events about load balancing decision only ocurs once per connection.

Use HTTPWatch, Fiddler, or something similar, to capture what happens when transferring files. What URL the browser is trying to send the traffic. Also, check if you go directly to one of the servers the transfer works.