Thanks for the fast reply!
Unfortunately, I already commented out that exact, and all other os_printf functions as I mentioned above.
I also double checked it now (just in case).
I also forgot to mention, that I tried restarting my IDE, and deleting the core cache (path taken from verbose log) at:
%appdata%\Local\Temp\arduino\cores\a842aa3ed1b6a557f4ef2f1624d87ab8\core.a