I was facing a ‘Not found’ using alias/mod_alias.
The requested URL /home/ftp (…..) /index.php was not found on this server.
Alias "/ps/" "/home/ftpuser/ps/" <Directory "/home/ftpuser/ps/"> Options Indexes FollowSymLinks AllowOverride All Require all granted </Directory>
Apache was searching the file in /var/www/html/home/ftp
File does not exist: /var/www/html/home/ftpuser/ (...) /index.php
To solve it I had to tweak .htaccess and set RewriteBase.