Can you use the eShop on the Switch? N
If you cannot access the eShop, when was the last time/date you were able to? A few days ago
Did you restore a clean hack-free NAND before going online? Never restored
Do you get the error code 2181-4008 trying to update your games? N
Do you get error code 2137-7403 trying to update your system firmware? N
Can you login to Nintendo's website using your linked Nintendo Account? haven't tried
SX OS used? Y
Did you make an SX OS EmuNAND with a clean hack-free NAND then stay offline with it? N (SX stealth-mode emunand used exclusively for NSPs)
Trimmed .XCI? N
Did you connect to the Internet with SX OS and/or to activate the license? Y
Did you play any .XCI files online with a certificate/header? N
Do you have a certificate/header ban (look for error code 2124-4025)? d/n
Lowest SX Version used when Online/Offline (NOT Switch System Firmware)? 1.0
What do you use Non-SX OS LayeredFS for? N
Did you connect to the Internet with a non-SX OS LayeredFS Inject? N
Played online w/ Non-SX OS Layered FS Injects? N
Did you inject an .XCI certificate using LayeredFS to play online? N
Used DevMenu? N
Installed any .NSP? N
Did you connect to the Internet w/ any .NSP installed? N
Did you play any .NSP installed online? N
Did you perform any CDN/Freeshop downloading with your own Switch's certificate? N
Did you update your .XCI/.NSP games online? Y
Did you ever use ReiNX? N
Homebrew/non-SX CFW Used? N
Connect to Internet with homebrew/non-SX OS CFW? N
Connect to eShop while using CFW/homebrew? N
AutoRCM? Y (long ago)
Did you update your firmware using ChoiDujour or ChoiDujourNX? N
Did you install the exFAT update offline? N
receive-lp1.dg.srv.nintendo.net blocked and/or "Don't Share Usage Information" ticked under "Other Settings"? N
Do you have eclct disabled (look for pm.kip under sysmodules/modules)? N
Do you have creport enabled (look for a folder named 0100000000000036 under titles)? d/n
What firmware(s) were you on when you cleared error logs prior to going online? N
Wi-Fi settings deleted in CFW? N
Console/Account Region(s) Europe
What device(s) do you use to send payloads with? computer, ns-atmosphere injector
Do you enter RCM by bridging pins 9 & 10 together? Y
tl;dr, I've used SXOS since initial release. Stayed strictly offline (no wifi settings) until stealth-mode was released. XCIs loaded while on sysnand(sxos), XCIs never played online, updated games in OFW. I only ever installed/run NPS and homebrew in SX emunand (stealth-mode enabled). Never run atmosphere, but have loaded Linux.
I'm surprised how long it took to get banned, over a year. I'd guess either a failure of SX's stealth mode (an XCI or NSP phoned home when loaded in SXOS), or Nintendo has inserted something in newer firmwares to flag consoles that load SXOS and that's phoned home in OFW.
At this point I think it's safe to say the only way to stay un-banned is to limit funny business strictly to offline emunand (unless Nintendo is doing something REALLY sneaky like leaving a fingerprint on the joycons or phoning home what RCM has been entered, which I doubt).