After nearly two weeks, it seems that Nintendo has finally fixed error code 2123-1502. The issue popped up just over ten days ago after firmware 12.0.3 arrived. When some players tried to download a new game or simply update a game that they already had installed, the error code 2123-1502 would pop up preventing them from completing their download.
The problem was pervasive enough that there were whole social media threads of Switch owners sharing cludge fixes to get around code 2123-1502. One involved messing with your DNS settings, while others required full system formats. Nintendo customer service referred users to their FAQs for network issues and informed angry Switch owners that they were aware of the issue and were working on a solution.
It seems that the solution has finally arrived. Nintendo Life reported several Switch users saying the issue is fixed on social media after Nintendo performed a server-side update on June 20. No details of the fix were announced, but Nintendo has a larger firmware distribution planned on June 28 that should forever banish error code 2123-1502.
Thank you, Nintendo. Now we can finally get back to Game Builder Garage.