I was hitting this same issue, but upgrading my install fixed it for me.

If you used homebrew like I did: brew upgrade bzt

EDIT:
it actually seems to be a different issue. When I clear the log folders it seems to work (or at least throws a different error)

EDIT 2:
Sorry for the double edit :p But I figured out the solution.

It looks like you need to use Python version 3.6.9 (or posibbly earler). But running the blazemeter tests on their cloud servers shows they use python 3.6.9. So I used that locally and it solved this bug for me.

Btw – if you haven’t used pyenv to handle local python versions I highly recommend 🙂