I have had this problem since the beginning, about a year ago. I'm on Horizon 7.13. This system was installed and setup by a consultant, first mistake. He was was given an impossible time line, second mistake. The problem is this. Almost all users are being directed to one Connection Server, I have two. It will not balance out the session between the two servers. I use a pair of UAG servers. Their connections are fairly balanced between them. They communicate with a load balancer in front of the Connection Servers. The load balancer has been checked twice and it's configuration verified by the vendor. I have talked to vmware support more than once and currently have an open case. Does anyone have any ideas why all sessions seem to gather on one Connection Server?
Most people here are from the community volunteeers, but I'm not sure even support would care that much, as long it meets the requirements. Unfortunaly I don't know much about ADC but you may want to look into any ip source based affinity. I'd review this, carl blog is usually pretty accurate
If I had to guess, your UAGs are in the same subnet and your source IP persistence is something else instead of /32 (255.255.255.255). This typically will result in both UAGs talking to the same Connection Server. Even if /32, there's still a chance that one went down and both started talking to the one of the Connection Servers, and source IP persistence made that stick. As long as you're under 2000 sessions per Connection Server, you are fine.
You can have your ADC team double-check that your Connection Server TCP-443/SSL VIP is set to /32 under the persistence settings: