Accounts "linked" using Kefir do not work with the last two or three updates to the NES and SNES apps. There is currently no way around this that I am aware of. It might be possible to copy a legitimate account from a clean NAND to your dirty NAND, but I haven't tried this since I already have a linked account on my dirty NAND from before it was dirtied.
Other than the above, you have two options:
- Use older versions of the NES and SNES apps.
- Use homebrew emulators, like Retroarch, instead of the two Switch Online apps.