I had this exact issue last week, all was fine then suddenly the client stopped going on and so applications never installed.
Anyway it turned out that my source files for the client had corrupted somehow (maybe A/V or an update?).
Check the source directory for files that are 0kb in size, and replace them with the proper sized versions from program files(x86)\system center configuration manager\client
And then update your distribution point.
If that's not it, on one of the failed deployments navigate to C:\windows\ccmsetup\ and retrieve the log from there for more info.