CSV import results in 504 gateway timeout

Hi,
I'm trying to import 2000 users from a csv to CB. Prior, I downloaded some users for the csv structure, added my users and saved it as comma separated utf-8 csv.
when I drag the csv to the CB import field, nothing happens for ages and then I run into a gateway timeout.
Some years ago I imported tens of thousands users into CB with no issues at all, any Idea, what's going wrong here?
 

That's probably too many users to import at once for your server. Break it up into smaller imports. Shared hosting environments will probably only tolerate 300 users at a time. Our import process isn't just a database insert it goes through the full object lifecycle. If you want straight database import you'll need to construct the queries for that yourself. In a future release we'll automatically chunk the import so it's done slowly with a progress bar as well.