The issue is caused by testing framework and stringification of large values when assertion messages are displayed. The problem does not occur when assertions pass, only failing assertions are a problem. A correct solution, which returns correct answers, should not time out.
I will think how to solve the issue and how to fix the kata, or the testing framework.

Can't stop getting timeouts for the c++ version.

I'm 99% sure it's not my fault because even when I immediately return std::string() from the function, I still timeout even though my function is doing absolutely no calculation. All the other tests pass perfectly fine and on my machine at home a 10k brainfuck source code computes in like 30 milliseconds

Simply returning an empty string immediately still times me out.

Really gave it your all, huh