CF2018u15 breaks xmlsearch and the resolution is to stop the service and rename/delete the cfclasses folder - the particular error is

coldfusion.runtime.CFPage.XmlSearch(Lcoldfusion/xml/XmlNodeList;Ljava/lang/String;)Ljava/lang/Object;

And I'll just say, once again, turn Save Class Files OFF -- it can cause a lot of weird problems (and it was Tom Jordahl who told me to turn it off -- he was surprised it was ON by default: it's the first thing I change on any CF server I setup!).