Mobile OAuth on Android suddenly not redirecting back from web browser

I've suddenly encountered a bizarre problem with OAuth login with my Android mobile app, wondering if this is just me or if it's a problem with Dropbox. The problem only occurs on Android (no issue with the iOS version of my app), and only if the Dropbox app is not installed (i.e. the login flow launches a web browser, not the app, to do the login)

I develop an app which allows users to login to their Dropbox account, so they can backup some app files to their Dropbox account. This feature has been in production, working flawlessly, for years.

All of a sudden, on Android, the login flow has stopped working, and I'm not sure why as I have not touched the login code for months. I'm using the Android SDK version 7.0.0. Here's what happens:

• The user taps a login button in my app, which calls Auth.startOAuth2PKCE(...)
• This opens the user's browser (the Dropbox app is not installed). They get to enter their username and password, and multi-factor code if enabled. This happens as normal.

• The problem is, after entering username, password and code, instead of redirecting back to my app which it used to do, instead I just get a blank web page in the browser, with the Dropbox logo and 'Sign out' at the top (I would like to attach a screenshot, but I don't seem to be able to)

I've repreduced the issue on both Android phones that I have access to, a Samsung Galaxy s22 and a Xiaomi 10T Pro, and the problem happens in both the development version and signed production version of my app. I've tried using both Chrome and Firefox as the default browser on both, same result.

Is anyone else experiencing the same issue? Can anyone suggest what might be happening here? I just can't figure out whats happening, because as I say, I haven't touched the login code in ages, and Dropbox Status says that everything is operational.

Thanks