We have a late addition to the Jade migration guide. I deprecated the use of the Eigen CMake Module in the cmake_modules package in Jade, but forgot to add it to the migration guide until @mikeferguson pointed it out to me. I've update the guide:
If you're using Eigen in your package consider reviewing how you find it in Jade and later.
Sorry for the noise,
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William Woodall
ROS Development Team