I am not very familiar with it (have published 1 small library and 1 PR to a large, popular framework), but when learning the language after having written most other things it felt like it had the most footguns and number of random rules you had to memorize + instances of undefined behavior.
I've never published anything with Ada (mostly because almost nobody uses it, so I've not had the same practical usecases) but I do follow the language passively and have experimented with it.
I feel much more comfortable that I could write a correct Ada program than a correct C++ program. I think I could write C++ for 5 years and not feel sure my program is entirely correct, even with IE "cppcheck", "clang-static-analyzer", "ASAN/TSAN/UBSAN" etc.
First, contracts are step one: they enable additional tools that can do static formal proofs using those contracts. It is impossible to prove anything about code that has a buffer overlow. In theory we have can write those tools without contracts, but the runtime for anything more than helloworld is unacceptable so nobody has even written them, contracts are believed to help bring that under control.
second, I assume only the latest modern C++ is used. I expect tools to give up as soon as they see constructs that are hard to analyze. (new/delete is obvious - but they reserve the right to add more constraints)
Third, modern C++ if you stick to only that is a lot easier to write safe code than C++98. Things are getting better - or where they are not we can treat them like rust treats unsafe - sometimes you need to do tricky things that tools can work with: isolate them to only those areas, have your best write the code, test it hard, and pray they work.
Fourth, conductive to bug free development is relative. I won't claim C++ will be the most conductive to bug free code. Part of that is intentional: C++ aims to be useful in places where you are willing to make trade offs - if you are not willing to trade at least some productivity for runtime speed C++ is not the right language for you.
Note the last: I never claimed it will be better than Ada/Rust/whatever. I have no experience with either, but tend to believe those who claim they are more productive.
I maintain a lot of C++, which interoperates with other C++: adding another language is probably lower productivity than writing more C++ in the long run just because those interfaces between languages tend to be where things are the hardest. So I'm taking a different approach: getting involved with the C++ standard to attempt to make it more productive.
> So I'm taking a different approach: getting involved with the C++ standard to attempt to make it more productive.
I think both Airbus and Boeing have been doing their best to demonstrate the limitations of Ada and Spark.