My cargo installation was silently failing to work, because the API endpoint was stuck in a redirect loop (T215857).
I think Cargo should surface API errors/timeouts when it has problems, especially in the maintenance scripts.
At first this seemed like a cargo problem, because the whole wiki worked otherwise. It was just when I clicked create table on a template that it would time out, and the table never appeared. Running the maintenance script from cargo even with --mwdebug produced no error messages, but also no cargo table.
It didn't seem like a permission issue because maintenance/update.php created the two initial cargo tables just fine. And SMW worked fine all this time as well (obviously it does not use the API).
I then had to use the dev tools in Edge (corporate network, I know) to spy on the network ajax calls, which is when I saw the API call. I then curl'ed the API call and finally got the error message, which, unfortunately for me was a bit cryptic and led to me having to dig into api.php code.
All this to say Cargo should surface these errors, and likely timeout faster too.
Otherwise, thanks for the great extension!