Some errors get reported as NativeMap with minified stack traces

Some of our errors get reported in a format like this:

{ NativeMap: {"stringified":"TypeError: Cannot read property 'filter' of undefined","name":"TypeError","message":"Cannot read property 'filter' of undefined","stack":["TypeError: Cannot read property 'filter' of undefined","    at Object.<anonymous> (mailworker.bundle:41:13348)","    at p (mailworker.bundle:8:419)","    at Generator._invoke (mailworker.bundle:8:1739)","    at Generator.t.<computed> [as next] (mailworker.bundle:8:841)","    at l (mailworker.bundle:9:1810)","    at f (mailworker.bundle:188:154)","    at mailworker.bundle:188:881","    at mailworker.bundle:193:1778","    at y (mailworker.bundle:193:660)","    at C (mailworker.bundle:193:1024)"],"error":{}} }

This is happening even though we’ve uploaded the files and the sourcemaps for the mailworker code. We are using RN Sentry 1.0.6. All of the errors I see are coming from our Android app.

Sample error:

Any idea why this is happening, and how we could fix it? We would like to see a sourcemapped stack trace so we can tell what the actual issue is.