The way it works, is if you have two servers that are in a server group, the first one will be used until it becomes unresponsive. If it becomes unresponsive, the second one will be used exclusively and the first one will be marked down. If there is only a single server in the server group, even if it is unresponsive, it will NEVER be marked down and the controller will continuously try.
Here is what I would do:
- Try using the "good" server in the server group as the first server and put the "bad" sever as the second and see if you have any issues (a week?). If don't have any issues, switch them. The only way to find out if a server is at fault is to leave it by itself in the server group and then look at the server logs that correspond to the time that it timed out.