I was able to solve this problem just by running this in a command window with admin privileges:
activate <env-name>
conda update pip
After that, exports of the available packages on my environment contain again both the packages installed with conda and those with pip.
I suspect I may have caused this package export problem because I had followed the instruction that pip gave earlier on, when I was executing a package install:
“You are using pip version 9.0.3, however version 10.0.1 is available.
You should consider upgrading via the ‘python -m pip install –upgrade pip’ > command.”
So updating with python -m pip install --upgrade pip broke my package exports, but conda update pip fixed it.