find_package does not find Boost

Our project is building and running on Windows 7 and Ubuntu 16.04. I am now trying to cross compile it under licensed code, copying our project under the external directory. I added BOOST_ROOT, BOOST_INCLUDEDIR and Boost_DIR to the terminal but they get stripped from the environment.
I have:
cmake version 3.15.3

Boost is in:
/usr/local/lib/cmake/Boost-1.71.0/BoostConfig.cmake
/usr/local/lib/cmake/boost_XX-1.71.0 folders
/usr/local/lib/libboost_XX.so.1.71.0 files

The top of my CMakeLists.txt file, including diagnostics:
cmake_minimum_required(VERSION 3.12)

project(MyProject CXX)
message("Running CMakeLists for MyProject!")
# Options
option(GEN_DOCS "Generate documentation" OFF)
option(BUILD_TESTS "Build test executable" ON)
option(INSTALL_LIBRARY "Install the library" OFF)
message("(env)BOOST_ROOT is $ENV{BOOST_ROOT}") #2020-01-14
message("(env)Boost_DIR is $ENV{Boost_DIR}") #2020-01-15
if((${CMAKE_SYSTEM_NAME} STREQUAL "Linux") AND (NOT DEFINED BOOST_ROOT))
    message(STATUS "setting boost_root for Linux")
#    SET(BOOST_ROOT "/usr/local/lib/cmake/Boost-1.71.0")
#    SET(BOOST_ROOT "/usr/local/lib/cmake")
#    SET(BOOST_ROOT "/usr/local/lib")
    SET(BOOST_ROOT "/usr/local")
endif()
message("BOOST_ROOT is " ${BOOST_ROOT}) #2020-01-15
find_package(Boost 1.71.0 REQUIRED COMPONENTS system date_time filesystem)
message("Boost_FOUND is " ${Boost_FOUND}) #2020-01-15
message("Boost_INCLUDE_DIR is " ${Boost_INCLUDE_DIR}) #2020-01-15
message("Boost_DIR is " ${Boost_DIR}) #2020-01-15
message("Boost_CONFIG is " ${Boost_CONFIG}) #2020-01-15
message("Boost_VERSION is " ${Boost_VERSION}) #2020-01-15

The output includes:
| Running CMakeLists for MyProject!
| (env)BOOST_ROOT is
| (env)Boost_DIR is
| – setting boost_root for Linux
| BOOST_ROOT is /usr/local
| CMake Warning at /home/me/dev/source/github/MyProject-build-yocto/—/usr/share/cmake-3.12/Modules/FindBoost.cmake:577 (message):
| Imported targets and dependency information not available for Boost version
| (all versions older than 1.33)

and farther down
| CMake Error at /home/paradigm/dev/source/github/MyProject-build-yocto/—/usr/share/cmake-3.12/Modules/FindBoost.cmake:2048 (message):
| Unable to find the requested Boost libraries.
| Unable to find the Boost header files.

and farther down
| Boost_FOUND is 0
| Boost_INCLUDE_DIR is Boost_INCLUDE_DIR-NOTFOUND
| Boost_DIR is Boost_DIR-NOTFOUND
| Boost_CONFIG is
| Boost_VERSION is

Is there another way to link to the Boost libraries? Can there be incompatibilities between the cmake program and modules of another version?