Core.getLogNode(String) method has been deprecated for quite a while (since one of the first 2.5 versions I think), and has been replaced by the
Core.getLogger(String) method ever since. Apparently Mendix finally removed the old method in the 3.0.0-rc1 release.
Note that most IDEs (like Eclipse) give deprecation warnings when your code is using deprecated methods; although these are 'just' warnings, you shouldn't ignore them.
"results in a lot of java errors" where...? Compilation in the modeler? Eclipse? Running in the cloud? On premise? The question is pretty vague :)