we noticed that you can set your Deployment Target to a system that will not support the selected C++ version. An example: C++14 against OSX 10.8. The plugin will build, but it will not load under OSX 10.8.
EDIT: After some tests, the issue is related to a JUCE module that requires 10.9 as minimum target, while the C++ version is not causing any issue.
It will be very useful to have Projucer warning you if such condition is met.