I thought I had edited my previous post, however it may not have gone through. Long and short, I googled “vaadin Servlet 3.1+ is required” and went to the release notes: https://github.com/vaadin/platform/releases It is spelled out for me there, V10 requires WLS 12.2.1+. Moving on with the second option of downgrading the application to V8.
Thanks,
Steve