Hey Matthias,
Sorry to hear this!
I cannot recreate this discrepancy, so I’m wondering if perhaps your outdated version of The Events Calendar is related at all here. To test this, please update your site’s version of The Events Calendar to its most recent version, which as of now is 4.3.3
If that doesn’t help, then I’m curious: can you identify any sort of pattern for the events on which the View Details link doesn’t show up? Is it only events where the attendee didn’t add info, for example? Anything at all you can identify as something they have in common…?
Thanks!
George