I was running a 32-bit version of GCC while compiling. Upon compilation, the 64-bit pointer I defined was being partially cut to accommodate the 32-bit nature of the compiler.

After upgrading to a 64-bit GCC version using the UCRT64 environment provided by MSYS2 (command below), the issue was resolved.

pacman -S mingw-w64-ucrt-x86_64-gcc