None is None, not S0, you are confused.
S0 is a different type of security, the first security available on Z-wave and it should be avoided.
None is no security.
The mobile app, you would have had to have scanned the QR code into the smart start list. That is the only way a device could include by itself as S2 Auth without you typing in the DSK. As long as its in the SS list it will just keep rejoining every time you exclude it.
Fo sho - count me among them!
Ok .. thats still weird cause like i said .. they are all the same kind of switch.
I do not think i used the qrl code on any of them .. i think ,, its been awile now ..
i entered the numbers. on the code. on all three.
That maybe true .. but because of my system setup .. they were getting very high Route Changes
Like 15-30 times per few days. and would kick in and out of working.
Sooooo .. I thought I would try NO security just for testing.
Or I am just going to replace all of them with zibee .. but This cost 0.0$ to try 
I still have all zwave with no security (47 devices I think) plus my Alfred lock on S2.
I have all my zwave on my C7 with external antennas. That’s one think that @WarlockWeary didn't mention - what hub are you on?
We are moving next year. I will upgrade my hubs at that time.
I know I have also read comments from @jtp10181 and others that the error correction is better with S2, especially for battery operated devices. I don’t have any errors so in my opinion simple is better.
I have double the # of zigbee devices but I would take zwave over zigbee any day.
Edit : I would make this an excuse to buy more zwave btw and strengthen that mesh 
JTP gave me that same advice when my Zooz ZSE44 temp sensors were giving me random bogus readings, and I am using them for my HVAC system, so they HAD to be correct.
Switching them to S2 has made their reporting rock solid since then!
Giving credit where its due, I believe it was @coreystup who was originally voicing the advantages of S2 and explained it in a post. I just regurgitated it and had a few people test it out, and confirmed that it did in fact result in less erroneous readings from sensors.
Ah! You shattered my image of you 
Yes....SO disappointed!!! 
Still, JTP, you have helped me so very much in the past, but yes, credit goes to coreystup.
You should see him w/a chainsaw in his hands...image restored, x's 10.
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