Thank you for your answer.
Hmm. Okay. You'll have to hold my hand here a little as you know much more about this than I.
So I should remove and re-ad the S2 devices and be sure to skip the S2 inclusion then?
As far as the other information about the hops and latency, what can I do with that information exactly? I can't manually map things as I understand it.
What's also weird, looking things again is stuff like this:
[Dining Room Chandelier] None 01 -> 0F -> 12 -> 0B -> 0A 100kbps
[Dining Room Potlights] S2 Authenticated 01 -> 0B 100kbps
These two switches are in the same gang, so about an inch apart. The S2 device goes straight to the hub. The Chandelier, however, goes:
Hub -> Eating Area Chandelier -> Entrance Chandelier -> Dining Room Potlights -> Dining Room Chandelier
It should be able to connect directly to the hub as it is the same distance as the potlights but instead it is going to the kitchen light which is in the middle of the home, them the entrance light, which is way at the front, then all the way back to the switch next it... You don't know the lay out of my home but the signal basically goes the entirely wrong direction, then turns around and hops backwards. I struggle to see how that could possibly be the best path given the switch next to it can reach the hub directly. Or why does it not connect to hub directly from the switch next to it, versus adding 2 more hops in between.
It's difficult to provide a recipe for these things and that's why there's a tendency to say "Add repeaters" because often that does solve the problem. You can buy a couple of the Ring or Aeon (or others) dedicated repeaters that just plug in the wall. Click repair on some of your worst devices and see if the repeaters help. If not, reposition them and try again.
But understanding the challenge the radios have in communicating is often a first step. The hub, in working out the routing table has no information that indicates direction. Two devices sitting side by side in a 3 gang box look identical to two devices in opposite directions on different floors of the house. The RSSI value is going to be the same in that example. The result is, many devices will be told to route through what we would imagine is the craziest path.
Everything attenuates RF signals. Walls, furniture, everything. Obviously metal will attenuate more than many other materials and none of use can see RF and can't tell that there's a 1/2" water pipe in that wall that is perfectly aligned to block a path. Air ducts are easier to imagine because they are big metal. But one funny story I remember was caused by a mirror.. yea, aluminum metal behind glass... when person A would use the tilt-able mirror, the room lighting worked perfectly. 15 mins later, person B used the mirror and all the lights quit working. The tilt angle apparently caused the RF signal to be attenuated. You can imagine that tilting it made the wooden frame higher or lower. When low, the RF hit the wood and sailed right past, but when higher, the RF hit the mirror and went nowhere.
Only you know your home and what path the RF is taking. Recognize that a mesh has a goal of being a bigger sphere and will often route through an edge device hoping to pick up devices beyond. Then that device become the edge to be routed through...
Thank you for your help! That's really something with the mirror impacting things as drastically as that!
I guess I am still scratching my head as to why two switches in the same gang as acting so differently....
I guess, before I go out and spend money on repeaters (which, if I have to, I will) I want to exhaust all other options. Would adding and re-adding (as unsecured) my S2 devices be a worth while step, or should I just bite the bullet and add a few repeaters?
It depends on when you paired each switch. If one was done later it could have grabbed a different route initially.
Note: The thing to remember is these devices are not really aware of their physical location/position relative to the hub - they base it on the "best" signal strength & route potential + some other dark magic (probably).
You'll have to balance the "purchase now, return later" path vs trying the S2 -> None path. For me, the tasks of initiating a return, printing the label, packing, driving to drop off would prevent me from buying early... but you might be visiting UPS everyday and one more package is no big deal. 
You have 4 devices with negative RSSI values and I can't see how S2 -> None will help them. Dedicated repeaters are fun because they just plug in the wall and can be moved so easily to find where a repeater will do the most good.. I used that method to find where to add an In-wall outlet. My family thinks those things plugged into the wall outlets are 100% optional and they will unplug them and toss them in a drawer. So those locations get the outlet swapped to a ZWave outlet, even though nothing is plugged in 90% of the time and I have no automation need for them. I have a Rule for keeping the outlets turned on, so that they function just like the dumb outlet. My dedicated repeaters are now in closets and behind furniture that prevents them from being unplugged.
Thank you both.
All 20 dimmer were installed on the same day - I made a Saturday of it 
I did install them sequentially so I suppose there a difference of a few hours from the first the to the last. I also appreciate the dark magic comment! HA!
I am in the exact same boat @csteele with regards to returns. It's a pain that I would rather avoid. I did remove and re-pair 2 switches that were S2 today and they seem to be working better my issue was inconsistent/intermittent - As I gaze around the room looking for a mirror - so I will keep an eye on things but so far, it's promising.
I also love the idea of adding ZWave outlets in place of repeaters. That's a great solution; thank you! What's a little disappointing, for me, is that my home isn't that big and I have 20 switch. Everyone of them has another switch within eyesight (ie a totally unobstructed view to the next switch) so I really was hoping for a better result. Hopefully removing the security will do trick.
I shut down the Z-wave repeater on all my Iris 3210-L and find I still need repeaters in some locations, particularly near outside (Inovelli) outlets.
Whose in-wall outlets do you prefer? The GE are only around $40. Some others are too much $$$.
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