I believe I found the issue; it's apparently a problem with the Windows build of libuv. There's a pull request that mentions this issue and proposes a fix, but it's several years old by now and has likely been forgotten about.
Unfortunately, I'm not experienced enough to compile C++ projects...
I use Windows for development and I noticed that Ctrl+Space isn't being passed correctly to Neovim within my terminal (Windows Terminal 1.19.10821.0).
I have mingw installed, which includes cat, so I used cat -v to see if the ^@ character is being passed into applications, or just being ignored...