As far as I can tell, the definition of C++ is mostly driven by compiler folks (and wannabes), motivated to add features for their own career benefit and generally doing so in the way that's most convenient for them (e.g. std::move as a pseudo-function instead of as real syntax that the already-insane parser would have to handle). Since only the in-group's interests are considered, the much more numerous regular C++ users are ill served.
For all its faults, there's much less churn in the definition of C and what change does occur seems to be driven by clearly demonstrated needs out in the real world. C might seem stagnant, outdated, incomplete, or unsafe - all fair criticisms - but at least a competent C programmer's hard-won knowledge of how to overcome these deficiencies doesn't get turned on its head every few years as a new language version comes out. Even decades-old C (at least since the K&R vs. ANSI function-declaration change) is still readable and scarcely less idiomatic than something written last week.
So, referring to the OP's title, which language has the bigger problem?