The release is key. When you said that you’re uploading sourcemaps to Sentry, this always happens in the context of a release. That means, that the sourcemaps are uploaded as “artifacts”.
Releases are typically named after a commit hash or app version. In your case, I guess it’s the commit hash.
Additionally, the release name (e.g. the commit hash) has to be sent along with all events that the SDK submits. For that reason, the SDK has to be configured with the release. Now, I haven’t looked at sentry-expo, but I imagine that it would work something like this:
dsn: 'your dsn',
release: 'release hash here',
To your last point: Isn’t the screen shot that you posted in the original post the stack trace? If there is no stack trace, then we can’t resolve anything. We do not parse stringified messages, so you have to capture an actual error.
If this is on sentry.io, can you link me to the issue so I can take a look, please?