As to falling back to any given language, that's not uncommon. Learning a new language is difficult, especially if the paradigms don't align well to what we already know, or have experience in. This may come down to experience, or it may come down to how you now think through problems. That said, I don't think that C++ is inherently more productive than Rust, I think saying your experience makes you more productive in C++ is a far more likely truth.
That has been my experience as well. Rust and the borrow checker get too much in my way. If I want a high level language I will use Python but if I want control all the way down to the hardware C++ is where I go. Plus, it /feels/ that ISO C++ has significantly picked up on momentum and is seeing more investments than Rust.
After each try with Rust, I ended up going back to c++ myself, it's just more productive in practice.