Yes - I discovered that when I did a barebones project without my fileTree dependencies, I had no issues. I'm going to pull those out and resolve them one by one...thanks.
You have an old and incompatible version of Tomcat on the classpath. Looking at your build.gradle, it must be coming from one of your fileTree dependencies. You should update their configuration to ensure that the only Tomcat dependencies on the classpath are those that are pulled in by spring-boot-starter-web. If you're not sure where the old Tomcat classes are being loaded from, running the app with -verbose:class will tell you.