The clang-format Dockerfile builds clang in Debug, it should probably build in Release:

https://github.com/Unibeautify/docker-beautifiers/blob/master/clang-format/Dockerfile#L19

-RUN cmake -GNinja -DLLVM_BUILD_STATIC=ON -DLLVM_ENABLE_LIBCXX=ON ..
+RUN cmake -GNinja -DLLVM_BUILD_STATIC=ON -DLLVM_ENABLE_LIBCXX=ON -DCMAKE_BUILD_TYPE=Release ..

Docker for some reason would be unable to compile and would kill the c++ process if its in Debug (it's also slower to compile)
More info here: https://llvm.org/docs/Docker.html