How to get reliable user feedback?

I'm doing a mobile application available for iOS and Android. Via our analytics tools we've identified some areas of the application where a significant amount of users drop off, but we don't know exactly why.

I've been trying to figure out how to gather reliable feedback from these users.

If they don't continue far enough to e.g. sign up as a user, we will not have any means to contact them, and they are very unlikely to leave feedback to our support, facebook, twitter, google play, or app store, or anything else.

If we were to ask a few friends to try out the app, they would just say "it's nice", and continue using it even if they don't like it because you're a friend.

If we were to pay a company to do testing, they would also continue using it, because they are paid to test it. They might report bugs, but I would find it unlikely that they would reliably tell us when the app makes users feel like they might not be interested or don't want to use the app, or why.

Do you have any ideas on how to get "real people" to give "real feedback", i.e. report those moments when you feel "fuck this shit, I'm uninstalling"?