My Firebase iOS App i had to put the frameworks in manually due to some reason in cocoapods.
i have been getting an crash error saying
2016-06-04 00
I just lost hours to this - the readme and documentation is really poor
You also need to include the GoogleToolboxForMac.framework I missed this out as I assumed it was for mac apps, but adding it in fixed the problem.
I was just dragging code files and frameworks from another project and encountered this problem. After adding all frameworks in build phase, adding -ObjC in 'other linker flags' solved the problem.