@ggordan Following most of these steps just solved my problem with this error: http://imgur.com/a/KUOQC - in particular step 2.

Thanks to @skellock for posting.

Thanks for the suggestion @zibs . Unfortunately, none of those steps seem to have worked. The file not found error changes from time to time. Right now it's something different, though the app builds and runs just fine.

Is DEAD_CODE_STRIPPING disabled for all your targets?

Do you have any 3rd party libs installed that haven't been upgraded?

@freakinruben DEAD_CODE_STRIPPING is disabled for Debug and Release.

@skellock All third party libraries have been upgraded, and the issue appears to be coming from within react-native libraries. Maybe it could be an issue with 3rd party libraries, but I imagine that in that scenario I wouldn't be able to build and run the app, which isn't the case.

The fact that it happens not all the time is even more strange.. But debugging this is a pain in the butt, I ended up throwing away the xcode project, workspace and schemes and recreating them, without much luck the first few tries.
Did you try deleting node_modules and downloading them again, making sure the ^ of the specified versions doesn't mess with the versions you want from npm?

@ggordan I've seen Xcode fail with that error before (blaming wrong lib) when I've had a 3rd party lib not upgraded AND when i've missed the new import statements up at my app level (both in the app & default test).

@ggordan Just found this solution which fixed issues for me with archiving a release with a different build-name than 'release'

@freakinruben thx for closing the loop! Something about Xcode was definitely off. I remember being able to compile in Xcode, but not the command line at one point. If I had hair left, I'd tear it out.

@freakinruben Thanks a lot for that. Managed to get it to archive

FWIW, I have $300 on the table for anyone that can figure out how to upgrade DiscourseMobile per:

https://discuss.reactjs.org/t/having-a-hell-of-a-time-upgrading-from-react-native-39-to-40/6331

@SamSaffron I'd like to help if no one else do that, I'm always using the bleeding edge version of React Native

@nihgwu sounds like a plan, should I update that topic to say that you are taking this? any timeframe?

Ok, I'll done in an hour or two, I suppose