Some permalinks are not working and show 404

Hi,
I’m using WP 4.2.2 on NginX with multisite (subdomain) installation and now I have a strange problem.
My new site has abaout 18 posts. And all links the the posts worked quite fine untill today morning. 2 of these links suddenly stopped working and showed an 404 Error page. With stopped working I mean they worked until today quite fine.

These things have I already tried:
– Proof if title and url are WP reserved keywords (they aren’t)
– Empty browser and server cache and try again (failed)
– Changed parmalinks settings to default (worked but I dont want that ^^)
– Edited permalinks settings to default, date, category and back to posts name (failed)
– Deaktivated all plugins (error is still active)
– Renamed post and changed url (worked)
– Renamed post and url, saved changes, undo changes and save again (fail)

I want to know what I have to change that the broken links works again. I don’t want to check every morning which links are broken and habve to be renamed.

NOTE: I have updated translations today morning. I’m not sure if the problem already existed before that, but I think so.