We had some issues in our CI where pipenv would sometimes fail to sync. It has recently gotten better, I think due to a fix of some race condition due to parallel installation. I think venv would be better suited for CI in general, since it allows the use of a simple requirements.txt file.

The other thing is I think it is rather slow, at least on windows which most of my team uses.

To conclude, I think as long as you aren't having any trouble and it simplifies your environment, you might as well use it.