I have a couple devices that have been for weeks showing a very high round trip time (RTT). Any ideas what can cause this and does having a couple devices with really high RTT wreck havoc on my mesh overall?
You'd be the best judge of that...are you seeing any issues w/your Z-Wave devices lagging or not responding promptly? The general rule is if things are working normally, don't worry about what shows in the Z-Wave Details screen or on the Z-Wave Mesh Details screen.
touché. I have quoted that myself in reply to others questions.
So yes I am occasionally seeing some odd delays on the Z-wave network. 95% of the time everything rects and responds very fast, but occasionally I see some bad delay, could be 3-5 seconds of delay. I am looking for things that could cause this. For example, I just replaced the one "S0" lock on my network and now with everything "None" except four door locks that are "S2 Access Control".
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My worst RTT avg is on an iBlinds that performes w/out issue, so at least in that context I'm not seeing any delays/performance issues that I've noticed.
Intermittent stuff like you refer to is the hardest to deal with...can we assume that the devices that are having the occasional delay are the ones w/the slow RTT values, or ?
Thanks, I think I will give the mesh a little time to settle with the recent removal of the S0 lock. Then see how my performance is looking and if other areas of improvement are needed.
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Sounds like a mature, and rational plan.
And of course most of us have never really been able to do that, so I wish you good luck. 
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There are many possibilities...
Here are a few (in no particular order):
RF interference / weak signal
Slow device (maybe by design)
Poorly functioning device
Low batteries
Not enough z-wave repeaters
Poorly functioning repeaters
Bug in hub z-wave stack
Bug in device z-wave stack
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LSS or FLiRS devices can also have unusually high RTT as in the case of @danabw’s iblinds.. These are not so much a concern.. But high RTT on listening devices is usually an indication of a problem..
@tony.fleisher did a great job of listing the most common, I would just add busy mesh: if you have a lot of fast reporting devices like power meters that are flooding your network.
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Just as a data point, I have a C7 hub in my utility room, which is chock full of metal, (ducting, HVAC, electrical panels, water heater, washer, dryer, large safe, and to top it all off, a steel beam and metal support post). This is also where I have a cell phone booster, and a fair number of Zwave and Zigbee devices.
My Zwave details report looks like signal hell. But, everything works. So as much as all that red bothers me, I'm just ignoring it! Lol
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I have a theory as to why.. 
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Yeah! I'd wondered what would happen. It turned out to be a definite microcosm of weird routing choices, abundant path changes, and crazy RTTs.
In truth, with all that metal, its a miracle it works at all. The multipathing is insane!
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Yep.. But, I’m a firm believer in: if it ain’t broke don’t fix it.. So if it’s all working for you, leave it alone..
So goes the plan. I am planning on extending the meshes out beyond the utility to cover the rest of the basement though. We'll see what happens as we add mesh nodes outside the Faraday cage. Certainly ought to be interesting!
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Wouldn't it be simpler to move everything inside your Faraday cage? Might be a little crowded, but think of the tiny RTTs you'd have!!
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