Create Doc failure

I’m having difficulty with the “Create Doc” process.

Admins can create a document via the WP dashboard (like creating a new page or post). These documents can then be edited by users. However, non-admin users wishing to create their own documents through the normal process cannot – on clicking the “Create Doc” buttons or links, the site appears to start loading a new page (the tab icon starts the loading “timer”), but nothing happens. If I leave it long enough (45 seconds or so), I have been getting a 504 Gateway Timeout error.

My context is:

BP Docs 2.2.3
BP 14.1.0
WP 6.6.2
php 8.2.24

The site is using the Astra Theme 4.8.2

I run another site on the same server with a very similar set of plugins and BP Docs works perfectly on that site. I fear it may be a plugin conflict, but since it’s a membership site with PMPro 3.2 (with the PMPro BP & BB AddOn 1.4.1), disabling these to check is out of the question (these are not on the other site).

Can anyone tell me whether this is likely? Or whether there’s a way round it? Or offer any help at all?

Thanks in advance,
Mark