Can WriteProcessMemory fail but report that it didn't?

Question

I'm trying to use Rust's Windows WriteProcessMemory in a project of mine in order to replicate the process hollowing technique. Although I use it in nearly exactly the same way in another place in the project, I'm having trouble getting this one to work. It looks to me like the whole buffer isn't getting copied to the location I enter, and/or the u8 integers are being squished into u64s when written.

The WriteProcessMemory call returns BOOL(1), which evaluates to true, and makes me think it is running successfully. If I provide the lpnumberofbyteswritten variable, it comes back as the same size as the shellcode buffer I intended to write. But the memory doesn't look right if I read it after writing, and the shellcode doesn't run properly (whereas in the other place in my project it does). Have I made a silly mistake? If so, does anyone see where?

Thank you!