APM site slowness/timeout

Your last description brings up some good points. I don't think we can rule out a monitor, or even a network issue at this point, but we can come close to eliminating what it isn't. You say this happens for internal and external users. Is there a common path that all users traverse? A router or switch? When it is failing, do you see the requests making it to the BIG-IP? If not, do you see them arriving at the device before the BIG-IP? Does it matter if you try to access by name or IP address? If you can verify that the request is getting to the VIP, then you can rule out network (and potentially DNS) issues.