libboost_system.a missing some symbols on release for linux platform

[linda...@gmail.com]

Hi boost team,

I build boost locally with b2 for boost 1.68.0. But I met an issue that I found libboost_system.a missing some symbols, for example: boost::system::detail::system_category and boost::system::detail::generic_category.
It only happens on Linux release, Linux debug is find and windows platform are good also.
And I checked my boost build 1.67.0, no this issue.
My compile command is:
./b2 cxxflags="-fPIC -Wall -Wextra -fstack-protector -Wstack-protector " -a --without-python variant=release link=static threading=multi toolset=gcc address-model=64 --stagedir=stage/$build_platform/release -d+2
./b2 cxxflags="-fPIC -Wall -Wextra -fstack-protector -Wstack-protector " -a --without-python variant=debug link=static threading=multi toolset=gcc address-model=64 --stagedir=stage/$build_platform/debug -d+2

Could you please help on this issue?
Thank you so much!

Linda