I am having issues similar to some previously described, but not able to get a workable solution yet. I'm sharing documents with external specific people, and the sharing process works fine with a link sent, and verification code process done, access gained.
There is no time limit set for the links, and initial access is fine, however if the email is clicking on again later (about a week) it asks for verification again, and if the URL is visited, then an error message is received: 'That didn't work. We're sorry but user@email can't be found in the blah blah directory.'
When clicking on 'Manage Access' for the files in question, they are still shared with the users. Surely users don't need to go through the verification process repeatedly? Isn't this the whole point of being able to de-select 'Require recipients to continually prove account ownership when they access shared items'?