Upgrading from 2.9.0.beta8 broke the site, unrecoverable

Hello and welcome @smileBeda :slightly_smiling_face:

Could you give us some more detail about your set up? For instance, what version you’re running, whether it’s a standard install, and if you have any plugins (official or third-party).

Normally upgrades go very smoothly, though taking a backup of a live site just beforehand is always prudent just in case.