Debug output from loaded library

Hello, I am working on a static library for use inside Unreal. I have the library loaded and can confirm it is callable, but I am unable to get ANY debug output (printf) from the library itself, looking in Output Log, Message Log & Session Frontend. Is there any way to get printf output from a loaded library? Sysinternals DebugView is also showing nothing.

Thanks for any help!

FYI - since printfs seemed to be consumed, I replaced my debug output macro to use a vsprintf function that would then write the resulting message to a file.