A possibly-related post: Sync Error: Restart and Upgrade Edit: Wrong link! I meant to post Some items cannot be decrypted - #2 by personalizedrefriger
However, because duplicating the note fixed the issue in this case, I don't think the issues are the same.
How can I identify which note has this problem using ID # f5586b5c7ff34db7a252c94af7a93352.
It's possible that a previous version of a note, a notebook, or an image/pdf/other resource (and not a note itself) is failing to decrypt. I think a previous version of a note would be labeled as a "revision" in the decryption error list.
Note that I'm currently working on a pull request that will show more information on the "items with disabled decryption" screen, so hopefully debugging such issues will get easier soon!