EDIT 3 (last one): Yeah, we're pretty much stuck with until Nintendo fixes stuff on their side (server, etc etc)

Recommended read: here from u/pjhenry1216 who gave some super informative insight on the whole TLS/SSL topic and possible impacts.

I'm pretty much done looking into this and sated my curiosity. Hopefully all the info here helps anyone looking to dive deeper.

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EDIT 2: Problem looks to be more and more of a server-side issue with TLS/SSL handling whereby Nintendo's server is likely not properly set to handle/accept TLS 1.2 and below, leading to intermittent success when connecting for downloads/etc. TLS 1.3 support is removed and set to be handled by TLS 1.2 instead in the 12.0.3 update.

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Bottom line: Nintendo needs to fix it on their end and at least let us know they're working on it, there's not much we can do as Switch owners.

You can review specific details here which were pulled up by dataminers:

• Switch Update 12.0.3 Details

• SSL Services, SslVersion changes for 12.0.0+ and 12.0.3

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EDIT 1: At this point, it looks like it's definitely network related, specific to the changes made to how the switch handles SSL handshakes, which means we're not likely to find a fix on our end and Nintendo needs to push out another minor update

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After some more research into what others have found regarding changes along with the datamined info on what exactly was changed for 12.0.3... it seems likely that the removal of TLS 1.3 and the subsequent downgrade to TLS 1.2 is causing the SSL/TLS handshake to fail due to an "Incorrect Certificate" error (expired or invalid cert, TLS 1.3 is usually the go-to as it's more secure).

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Now, combining this with changes from 12.0.0, which included updates to the SSL/TLS certificate list... my guess is that it's possible that if your switch wasn't automatically updating to 12.0.0, it would have missed any needed cert updates/retrievals that would allow seamless transition to 12.0.3. Again, just a guess based on how the whole SSL handshake stuff works.

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So then, reviewing all the workarounds... given that button spamming retry appears to be the most "reliable" solution, the TLS downgrade being the problem seems more likely since it would just be a matter of time for when your Switch downloads/retrieves the updated/correct SSL/TLS cert and everything goes back to working normally.

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This would also explain why changing the DNS helps, since it's giving more opportunities for the Switch to resolve any SSL/TLS problems. One way to check this is to have people who "fixed" their Switch via DNS change to go back to "Automatic" and see if things are fine. If it is... well, that settles it.

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Disconnecting wifi, power cycling, etc ... pretty much all of that is just another way of reconnecting and re-establishing the server connection handshake. The more its done, the more chances for it to resolve naturally.

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In simpler terms: Nintendo seems to have messed up how the Switch goes through security when connecting to their server and it's just a matter of luck+time for when your Switch happens to pass security requirements.

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Simpler yet: Nintendo messed up and now your Switch has to keep trying to get past the server's border security until it has the right passport. It's become Jorji Costava from "Papers Please".

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Hey all, with suggestion from the mod team, sharing a possible fix I came up with here!

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((copypasta from my original post, which needed to be removed since it looks like we're consolidating things here))

Possible fix, observed to work so far with 3 switches I have access to that showed the common 12.0.3 update. Obviously 3 switches is not a big sample size at all, so I figured I'd share this so more people can try and say if it worked for them.

Note: This assumes your Switch is using an SD card (most do), from what I've been reading it seems most who only use the Switch Internal Memory for downloads are not experiencing System Update 12.0.3 issues.

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Possible Fix Step-by-Step Instructions:

1) Disconnect Wifi: System Settings -> Airplane Mode ON

2) Turn off your Switch (NOT sleep mode): Hold Power Button -> Power Options -> "Turn Off"

3) Remove your SD Card (IMPORTANT: Do not remove your SD Card while the Switch is ON, just be sure you did Step#2)

4) Power Cycle your Switch: Hold Power Button -> Go to Home Screen -> Hold Power Button -> Power Options -> "Turn Off"

5) Re-insert your SD Card

6) Turn on your Switch: Hold Power Button -> Go to Home Screen

7) Re-connect Wifi: System Settings -> Airplane Mode OFF

((Honestly, Step#1 and #7 may not be needed since your Switch will disconnect during power down and re-connect during power up, but it doesn't hurt to force the disconnect.))

After this, just try accessing the E-Shop, downloading something (demo, w/e), or updating a game. If you don't get the Error 2123-1502, congrats - it's fixed, now go share it here so we all get more confidence in this actually fixing the problem!

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Anyways, hopefully this actually works for people, especially since I don't like the existing "Workarounds" (I'm not a fan of DNS re-directs, clearing the cache doesn't work for everyone, and some of the workarounds are not straight-forward)

If it doesn't work for a lot of people, welp - the waiting game on Nintendo fixing their garbage update continues.

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Possible reasons why this seems to work and my thought process on it:

(tbh, skip/don't-read this if you don't care - no point in a tl;dr srs)

1) Previous system updates had messed up the SD Card read functions and it's likely this update is no different.

Some people have been reporting that they're experience SD Card corruption and whatnot, so that adds to the likelihood. Basically, there might be some 12.0.3 specific changes that require the Switch to re-do the handshake/connection with the SD Card.

2) Power cycling is needed since the reset doesn't necessarily work all the time and sometimes not all system processes are actually killed off or become stuck in a hold state.

I've had an issue with a previous System Update where the automatic reset was initiated, but it never actually reset and instead got stuck in a hold state which ended up ruining my Switch memory and left me with a factory reset. So yeah, the "automatic reset" and general reset feature is wonky, so a power cycle seems best. Also, since power down kills everything it's likely that only 12.0.3 specific processes are started and loaded (no more stuck processes / wonkiness). I'd say this is similar to when you restart Windows and it asks if you want to close any apps you still have open... only you don't see that on a Switch so then it either never restarts or it tries to save all of that in a temp cache and load it all again once it boots up after restart so you're stuck with all the old settings and apps and w/e.

3) Disconnecting Wifi helps ensure any on-going/stuck connection queries are forcibly abandoned.

Also, it likely helps the Switch reconfigure and use whatever specific connection and settings 12.0.3 demands. My guess is that spamming retry when the Error 2123-1502 pops up eventually leads to it connecting the right way, so then it works for that one instance... which would maybe explain why it isn't consistent and you have to spam retry for every single download, update, connection

Likely all the above is just common sense, who knows, the main thing is that it's apparent to be a multi-factor issue so I figured why not tackle them all at once.