UPDATE 21/6/21: Nintendo has quietly performed network maintenance which reportedly fixes the dreaded Switch error code 2123-1502.
As spotted by Nintendo Life, a notice warning of maintenance taking place overnight last night was posted to Nintendo's Japanese maintenance website. Subsequently, fans affected by the error code have reported a return to normal service.
A Switch firmware update will also now follow, for release next Monday, 28th June.
At no point has Nintendo ever officially acknowledged the issue, beyond helping fans who have had to contact customer support.
We've been keeping a close eye on the problem - do let us know how you're getting on.
ORIGINAL STORY 18/6/21: Some Nintendo Switch owners are still reporting problems when trying to download games and game updates from the eShop, more than a week after the problem first came to light.
Nintendo customer support is aware of the problem, and there is a page of troubleshooting tips to follow if you encounter the issue's error code: 2123-1502.
Fans I've spoken to say customer support is helping as best it can, but that repeating the above "possible solutions" per-download is meant as a temporary solution at present.
Nintendo has yet to officially acknowledge the issue - Eurogamer got in contact last week but has not been issued a response.
Reportedly, customer support has told fans affected by the problem that a new firmware update is being worked on to solve the error for good.
Last week, a spate of reports flagging up eShop errors erupted after Nintendo released a small and otherwise unimportant system update. Rollout of that update was temporarily paused while Nintendo investigated issues, but then resumed.
Subsequently, some Switch owners were unable to download new games, updates and/or existing purchases from their store history. But not everyone has been affected, and some of the above solutions have solved the problem for a number of people.
If you're still struggling, it's worth checking trying the steps linked above, or checking in with the lengthy Nintendo Switch reddit thread on the problem where fans are sharing other DNS-switching tips.
Finally, here's another solution which has worked for some: