In version 3.3.1, /usr/share/cmake/Modules/Findassimp.cmake searches in /usr/local (as per upstream https://github.com/assimp/assimp/blob/master/cmake-modules/Findassimp.cmake) Just removing the file seems to fix the issue as it provides a /usr/lib64/cmake/assimp-3.3/assimp-config.cmake too
Updated. Thanks for your support