Cloner not cloning sites on nginx / Google Cloud Platform setup...

Cloner not cloning sites on nginx / Google Cloud Platform setup, I have no idea what's happening, whether it's a cloud server setup issue (as this wasn't an issue in our VPS setup / same site) or something else.

I click on Sites » [the sub-site] » Clone, and it gets to the grey screen with the "Cloning site..." title, yet nothing else happens after that. If I visit the supposed cloned site, on the front end, I get a 500 HTTP Error, if on the admin, I will sometimes get the same stuck Cloner (in progress) screen, although there's clearly nothing happening and no more bullet-points appearing (screenshot provided).

I need you guys to have a look please. I've granted access to support. I might need the support dev's IP to grant IP-level access since it's a project under development.

Thanks!