According to https://www.tutorialspoint.com/c_standard_library/c_function_sprintf.htm

the length should be "BEFORE" the specifier

in the above function (In the win32 version) the following is formatted

Poco::format(err, "Error %ul while loading [%s]: [%s]", errn, path, trimmedError);

and it should be

Poco::format(err, "Error %lu while loading [%s]: [%s]", errn, path, trimmedError);