This problem is caused by a known iOS linker bug, in which a static library category is not being loaded by Xcode, and is remedied by a small change to your BuildSettings.
Go to build settings.
In the "Linking" subsection, look for the "Other Linking Flags" key.
To "Other Linking Flags" add the value "-force_load" and the path to the "libXPush.a" file,
e.g. -force_load "$(SRCROOT)/libXPush.a".
This command loads all objects and categories in a static library and will solve the problem.