Scalability: "No app machine available to service LOGIN functionality in DBA domain."

[pgsteffen]

Running OTM 6.4.1, we have Scalability configured on two App servers, and two Web servers configured with F5 BigIP.
Using three URLs (App/Web pair #1, App/Web pair #2, F5 "common" URL) I am testing connectivity with the Apps servers in combinations of up/down states.

Testing scenarios and login results:

APP1 = Up
APP2 = Up
LOGIN all three URLs = OK

APP1 = Down
APP2 = Up
LOGIN all three URLs = OK

APP1 = Up
APP2 = Down
LOGIN all three URLs = No application machine is available to service LOGIN functionality in DBA domain.

APP2 = restarted
LOGIN all three URLs = No application machine is available to service LOGIN functionality in DBA domain.