Are you in the European Union? I am not sure but I recall curve only works there for card payments using the phone. Did you install curve via the play store? Some apps check the source of the app and change their behavior if not installed via the play store. Some banking or messaging apps don't like users on a VPN.
Does the Google play store and Google play services have network and notifications?
After that, I would clear the storage and cache of the curve app, so when you re-set it up, it'll forget any saved disfunctional data and maybe it'll trigger a reaction in Google services.
Many people don't use Google at all. Out of the Google people, only some use curve. That's probably why you haven't received a reply -- people that use curve haven't seen your post.
You could try giving Google and the curve app more permissions, like nearby devices.
If you don't receive an answer here, you could try the other GOS communities https://grapheneos.org/contact#community
Send a message during EU daytime hours -- it's midnight there now I believe. There is also a simplex community -- one of the biggest on simplex. There's probably someone on discord, matrix, etc to help that isn't on this forum. Some users might only visit once a week on the forum.
This post got rather long, good-luck mate! Let us know if you find the solution to help anymore curve people :)
Oh, lastly:
- the curve's logs under the apps info page could prove useful in revealing more information on the issue.
- you could try contacting curve and mention grapheneos.