You probably need to poll the endpoint, the status can take a few seconds to change.
There was a change in the Boulder (production/staging) code a while back that introduced occasional delays in that transition. The original ACME2 deployment never had those delays, so most clients did not poll after finalize as the certificate was always ready. IIRC, the pebble test server now temporarily hangs by default to ensure clients account for this possibility.
I don't see any deviation from normal in our Staging environment's metrics -- we're continuing to successfully finalize many orders. Without any additional info, like your client's User-Agent string, or the URL of the order that is stuck, there's not much we can do to help debug further.
It's a good idea to test with a few CAs because the differences can be good for flushing out this type of thing. e.g. ZeroSSL can be quite slow at some operations and (last time I checked) didn't cache validations.
I think (I might be remembering the wrong CA) DigiCerts finalize can take up to 10 minutes.