Nextcloud Webinstaller Code 504

Hy Guys, i‘m from Vienna so Sorry about my Englisch!
I have the Problem that after Installing NC23 the hole thing is lagy as shit!
I have my own vServer with Apache and Mysql running under Plesk 18!
The Installation runs smoothly thru but then when i trie to change something it brakes with an Codd 504!
Am i missing some thing?