F5 Load Balancing Exchange 2013

The slow ramp should not have any impact with the problem you described, this option is just to make sure a new server don't get overloaded when it becomes online. Imagine you have least connection, a pool with 10 servers it one has 1000 connections, another server in that pool comes online and will get all the next 1000 connections.

More information about slow ramp:

https://support.f5.com/kb/en-us/solutions/public/14000/800/sol14804.html

https://support.f5.com/kb/en-us/solutions/public/13000/000/sol13099.html

The reject action in the other hand looks to be related with the problem you described.