And even a brief news ticker:
Eben was a customer info, that the shop was suddenly no longer available. On closer inspection, it was no longer possible to any data access, are mapped to the domain (copied to e.g.. test.txt in the root directory no access to this file was possible).
The solution lay in an Apache Update, that certain entries in the .htaccess no longer allowed. In our case, it was an IP block with an explanation behind it like
Deny from 52.91.182.221 ##MauiBot ##
The information in the hashtags should be either above or below the command, but can not be more on the same line since the update.
Small problem with a big impact.